A number of things:

1. Dachau was one of the first and ultimately a prototype concentration camp (a large portion of concentration camp Kommandants served in some form or another in Dachau, making it something of a "murder school" as it is referred to in the relevant German literature). So the Dachau gas chamber was something of a test run later replicated at a larger scale in Auschwitz and the other death camps. https://www.mittelbayerische.de/zusatz/dachau-war-der-prototyp-fuer-das-kz-system-21681-art894539.html (in German)

2. Be careful when stating that the deaths were caused by disease rather than direct actions. It's an argumentation typically used by holocaust deniers. The fact of the matter is that work, malnourishment, and poor hygiene were deliberately induced as a means to slowly kill inmates. The distinction between direct execution most notably and the extermination through labor ("Vernichtung durch Arbeit" in German) is mostly semantic. Morally, the camp guards were completely responsible for the deaths caused by disease, malnutrition, and exhaustion. That was the intent. And the result was tens of thousands of dead. https://en.wikipedia.org/wiki/Extermination_through_labour

3. It's important to remember that the concentration camp system and the Holocaust itself didn't start out the way they ended up being. In fact, German historians typically divide the development of the camps into four phases: 1933-35 when they were under the auspices of the SA and housed political opponents, 1936-38 when they were taken over by the SS and other groups (Jehovah's Witnesses, homosexuals, "asocials") were interned (and in 1938, Jews in massive amounts), 1939-1941 when prisoners from conquered territories were interned (as well as Sinti and Roma) and the camps began to be used for "useful" work rather than just to work the inmates to death, and 1942-45 when the "Final Solution" was decided upon and the death camps were established. https://de.wikipedia.org/wiki/Konzentrationslager#1933_bis_1935 (in German)

4. So to answer your question: The determining factor for sending Jews to Dachau rather than extermination camps was which phase the internment occurred in. All surviving Jewish inmates in Dachau (and the rest of the camps in Germany) were sent to the extermination camps after Himmler ordered it on Oct. 5th, 1942. So in the long run, Jewish prisoners were not better off. https://www.dhm.de/lemo/kapitel/zweiter-weltkrieg/holocaust/dachau (in German)

Two of the most important determining factors were location and ability to work.

Jews from the occupied Eastern territories generally were not sent to concentration camps like Dachau, but rather were sent to ghettos, labor camps, killing fields, or extermination camps. And because there were not mass gassings at Dachau a Jew interned post 1942 had a moderately better survival rate, though not necessarily better living conditions. This is of course primarily because in many other situations, chances of survival were near zero. Someone in Dachau had a chance of survival, if you were sent to Treblinka or Chelmno, you were dead within hours of arrival.

In the final months of the war many more Jews were sent to concentration camps within Germany, such as Dachau, from camps like Auschwitz in Poland because of the approaching Red Army. Jews from Germany and other Western countries were at times interned in concentration camps, while Jews from Eastern Europe, the occupied Soviet Union, the Balkans, the Baltics, and Greece were near uniformly ghettoized, killed near their homes, or sent directly to an extermination camp. It would take surviving deportations through selections for labor, then survive a labor camp in Poland, then be transferred into the Reich for say a Polish Jew to end up in Dachau. Many French Jewish women were sent to Ravensbruk, before the war actually began many German Jews were arrested and sent to concentration camps, and the concentration camp/ghetto Theresianstadt was mostly Jewish. There were many determining factors in where someone was deported, and where they died, and sometimes it can seem horrifically random. But ultimately, most victims of the Shoah who died in camps rather than by bullets, gas vans, or in ghettos died in extermination camps like Birkenau, rather than concentration camps Dachau.

Part of the planning for Operation Reinhard, one of the largest parts of the 'final solution' was to create extermination camps which met the criteria of being on a major rail line, near large Jewish communities, but removed from prying eyes. The official Operation Reinhard camps were Belzec, Sobibor, and Treblinka. The other extermination camps, Auschwitz II Birkenau, Majdanek, and Chelmno, followed similar criteria. This meant that the Nazis often designated one camp to kill a Jewish community from a certain geographic area. For example the victims of Treblinka were primarily Jews who had been imprisoned in the Warsaw ghetto, as my family was.

The Reinhard camps were mostly used to kill Jews who had been in ghettos in the General Government in Poland, but there were deportations from across Europe. Generally a large number of people from a specific area ended up being killed in a single location over a relatively short period of time. When the Wannsee conference occurred, about 80% of Jews who would die were still alive, in less than two years, those numbers were reversed. Treblinka was the main killing center for the Jews of Warsaw. Belzec was used to murder the large Jewish population of the Lublin district and southern Poland, as well as those of Lvov and Krakow. Additionally Jews from Germany, Austria and the Czech Republic were deported to Belzec to be killed. Sobibor was built along the Chelm-Lublin rail line and was used to kill Jews of the Northern and Eastern sections of the Lublin district as well as from occupied areas of the USSR, the Netherlands, France, Austria, Slovakia, Bohemia/Moravia, and from within Germany itself. These three camps alone had a death toll of around two million. These camps also had extremely low numbers of survivors. Sobibor had 58 recorded survivors, and this relatively high number is only because of a mass escape. There were less than 10 survivors of Belzec and about 70 from Treblinka, again due to a mass escape.

The death camp at Chelmno was used to murder the Jews of Lodz, as was Auschwitz. There were only three survivors of Chelmno, all men who escaped. All of these camps were also used to murder Jews deported from other areas. Auschwitz was the most "international" camp being used to kill Jews from all around Europe. Over 1 million were killed by the Einsatzgruppen in mass killings. In these cases Jews were generally killed and buried near where they had lived. In other cases they were deported to killing fields in places like the Ponar Forest, and Riga, Latvia. The numbers can be staggering. In three days, over 30,000 people were shot in Babi Yar, a ravine near Kiev. In Birkenau and other death camps the death toll could be over 6000 a day at certain points.

Those who were sent to concentration or labor camps like Dachau, were generally, though not exclusively, Jews from Western Europe, or who were chosen for forced labor. Those chosen for labor were generally sent to labor or concentration camps from cities or ghettos, sometimes while ghettos were being liquidated. Depending on how long they survived they might then be transferred between labor and concentration camps. They would die of starvation and disease, or by execution, or by deportation to a killing center, but they had a better chance of survival than those sent straight to extermination camps. For example Plaszow, the labor/concentration camp depicted in Schindler's List primarily housed Jewish prisoners who were chosen for work from the Krakow ghetto while the ghetto was being liquidated and transports were being sent to the death camps of Belzec and Auschwitz. It was converted to a forced labor camp and at multiple points large proportions of the prisoners were executed or deported to Auschwitz. At the end of the war death marches sent some of the prisoners to Western concentration and labor camps.

Auschwitz-Birkenau alone accounted for about 1- 1.5 million of the six million Jews killed, another 2 million were killed in the three Operation Reinhard camps, and another million at least were killed by the Einsatzgruppen, together this accounts for the majority (4+ million out of 6+ million victims) of the dead. The rest were killed in ghettos, labor camps, in concentration camps, while attempting to hide or escape, and some were killed in combat as part of Jewish partisan units.

https://encyclopedia.ushmm.org/content/en/article/operation-reinhard-einsatz-reinhardThe Operation Reinhard Camps by Yitzak AradBlack Earth and Bloodlands by Timothy Snyderhttps://www.yadvashem.org/holocaust/about/final-solution/death-camps.html