This is not a unique case. Another camp commander who was tried and convicted for misconduct was Karl Otto Koch, the first commander of Buchenwald. He was executed in early 1945 for embezzlement and the unlawful murder of three prisoners.

The purpose of concentration camps was not "to get rid of as many undesirables as possible". That was the purpose of the death camps. See this comment for the difference between the two. And the only people sent to death camps to be gotten rid of were Jews and Gypsies.

Concentration camps were prisons and originally, from 1933 to 1939, they were prisons for German citizens only. As such, they were subject to rules and regulations. There certainly was a lot of brutality, sadism and random killings, but in theory none of that was allowed. And sometimes the SS, which had its own courts in which it tried those of its members that got out of line in one way or another, deemed it necessary to bring those involved to trial. There were two main things that could get you in trouble: financial shenanigans, and tarnishing the reputation of the SS.

The SS liked to see itself as an elite organisation whose members laboured selflessly and honourably for the good of the Reich (state) and the Volk (people). Even when they were shooting or gassing millions of Jewish men, women and children, they were doing so not out of base motives or bloodlust, not like crazed killers, not sadistically, but in a disciplined, detached manner, because it was necessary for the survival of the German race. That is what they told themselves. Here's Himmler addressing an SS gathering in October 1943 (bolding mine):

I want to also mention a very difficult subject ... before you, with complete candor. It should be discussed amongst us, yet nevertheless, we will never speak about it in public. Just as we did not hesitate on June 30 to carry out our duty as ordered, and stand comrades who had failed against the wall and shoot them -- about which we have never spoken, and never will speak. That was, thank God, a kind of tact natural to us, a foregone conclusion of that tact, that we have never conversed about it amongst ourselves, never spoken about it, everyone ... shuddered, and everyone was clear that the next time, he would do the same thing again, if it were commanded and necessary.

I am talking about the evacuation of the Jews, the extermination of the Jewish people. It is one of those things that is easily said. [quickly] "The Jewish people is being exterminated," every Party member will tell you, "perfectly clear, it's part of our plans, we're eliminating the Jews, exterminating them, a small matter". [less quickly] And then along they all come, all the 80 million upright Germans, and each one has his decent Jew. [mockingly] They say: all the others are swine, but here is a first-class Jew. [a few people laugh] And ... [audience cough] [carefully] ... none of them has seen it, has endured it. Most of you will know what it means when 100 bodies lie together, when 500 are there or when there are 1000. And ... to have seen this through and -- with the exception of human weakness -- to have remained decent, has made us hard and is a page of glory never mentioned and never to be mentioned. Because we know how difficult things would be, if today in every city during the bomb attacks, the burdens of war and the privations, we still had Jews as secret saboteurs, agitators and instigators. We would probably be at the same stage as 16/17, if the Jews still resided in the body of the German people.

We have taken away the riches that they had, and ... I have given a strict order, which Obergruppenführer Pohl has carried out, we have delivered these riches [carefully] to the Reich, to the State. We have taken nothing from them for ourselves. A few, who have offended against this, will be judged in accordance with an order, [loudly] that I gave at the beginning: he who takes even one Mark of this is a dead man. [less loudly] A number of SS men have offended against this order. They are very few, and they will be dead men [yells] WITHOUT MERCY! We have the moral right, we had the duty to our people to do it, to kill this people who would kill us. We however do not have the right to enrich ourselves with even one fur, with one Mark, with one cigarette, with one watch, with anything. That we do not have. Because we don't want, at the end of all this, to get sick and die from the same bacillus that we have exterminated. I will never see it happen that even one ... bit of putrefaction comes in contact with us, or takes root in us. On the contrary, where it might try to take root, we will burn it out together. But altogether we can say: [slowly, carefully] We have carried out this most difficult task for the love of our people. And we have suffered no defect within us, in our soul, or in our character.

In light of this, I would like to present the case of SS Untersturmführer Max Täubner who was court martialed in May 1943 and sentenced to ten years, expelled from the SS, and deprived of his civil rights for an additional ten years, for

a) three unauthorized mass killings of jews, and in particular the excessively violent and sadistic manner of the third mass killing – although the court recognised that "the Jews have to be exterminated and none of the Jews that were killed is any great loss", nevertheless "the accused allowed his men to act with such vicious brutality that they conducted themselves under his command like a savage horde".

b) taking pictures of mass executions and showing them to family and friends while on leave.

c) the unauthorized killing of a Ukrainian militia man.

Täubner was tried because he broke his oath of secrecy on the killings (the Holocaust was Geheime Reichssache or a state secret), because he allowed and encouraged his men to behave in a manner unbecoming to elite SS members, and because the killings were unauthorised: they were not scheduled and ordered but done on his own initiative. There were rules and regulations to be followed even in the process of exterminating the Jews.