It seems to me that if the Armenian genocide is going to be recognized as a genocide (as it generally is, and ought to be), so too should the Nazi genocide of Slavic peoples in WWII. There were specific German plans to eliminate the Polish people (through mass murder, slavery, liquidation of Polish culture, and the integration of a small minority of 'racially valuable' Poles into German identity) and these were partially implemented, hence something like 3 million non-Jewish Poles died in WWII. And then there is the deliberate starvation and extermination through labor of millions of Russian POWs.
Let me start by pointing to a fundamental problem with the way this and other similar questions are phrased: They rest on the perception that because you haven't heard/read about it, it isn't talked about. Which in most cases, including this question, isn't the case in the vast majority of all cases. Plus, when not specifying where these aren't allegedly talked about (in the US? In schools? In historiography of Nazi Germany? In you circle of friends? On the internet?), these questions are virtually impossible to answer and come off like more of an attempt at complaining about things rather than a genuine question. No historian can tell you why in the social situations you find yourself in, this isn't talked about more because we don't know who you are, what you are education is and what kind of social situations you find yourself in.
What I can tell you that unlike your assertion that it isn't talked about, these subjects have been issues of English-language and other historiography for decades and have been explored in great detail. In German historiography the Nazi murder of and policy towards Poles has been explored in detail going back to 1961 with Martin Broszat's Nationalsozialistische Polenpolitik. 1939–1945. In 1981 Czesław Madajczyk wrote Die Okkupationspolitik Nazideutschlands in Polen 1939–1945. to great acclaim. More recent works include 2008's Anna Meier: Die Intelligenzaktion: Die Vernichtung der polnischen Oberschicht im Gau Danzig-Westpreußen; Dieter Pohl's 2009 collection Der deutsche Krieg im Osten 1941–1944. Facetten einer Grenzüberschreitung; and 2006's Jochen Böhler: Auftakt zum Vernichtungskrieg: Die Wehrmacht in Polen 1939
The United States Holocaust Memorial Museum not only has part of their exhibition dedicated to Nazi policy in Poland and the USSR, they also provide entire bibliographies for the English-language historiography online: Here on the subject of Poles, including the highly recommended Tadeusz Debski: A Battlefield of Ideas: Nazi Concentration Camps and their Polish Prisoners. from 2003 but missing the also highly recommended Martin Winstone The Dark Heart of Hitler's Europe. Nazi Rule in Poland under the General Government.
Unsurprisingly, the most extensive body of scholarship comes from Poland with examples such as Maria Wardzyńska: Był rok 1939. Operacja niemieckiej policji bezpieczeństwa w Polsce. Intelligenzaktion. from 2009 or the numerous publications – sometimes of varying quality – by the Institute of National Remembrance.
Similarly, Nazi German policy in the Soviet Union and the crimes committed against Soviet citizens is something that has featured majorly in historiography at least since the publication of Christian Streit's Keine Kameraden about the crimes against Soviet PoWs in 1978, and has continued since then, especially in the context of the German Wehrmacht exhibition and with the opening of Soviet archives. There is virtually too much to list here in terms of literature but authors like Dieter Pohl, Alex Kay, Lorna Weddington, Wendy Lower, Timothy Snyder, and Omer Bartov have all written fairly high profile books on this subject in very recent years. Here you'll find a post of mine on the General Plan Ost, including some more literature about it.
Even in the most common and widely available literature that discusses overall subjects like Broaning's The Origins of the Final Solution, Mark Mazower's Hitler's Empire. and Richard Evan's Third Reich trilogy, all these subjects are discussed prominently and with apt references to the vast literature on these subjects. If one went to look for gaps in research on Nazi policies of occupation and Nazi policy towards occupied subjects, Poland and the Soviet Union isn't it. Compared to say, Albania, where there is virtually only one (1!) English-language book on the occupation by German forces or to, say, Serbia where it's only been recently that a comprehensive overview of the occupation was published in 2017, there certainly is more to explore in connection to Poland and the Soviet Union but it is an incorrect assertion that it is a topic that is not discussed or researched, simple as that (also, Polish civilian victims are comprised of 3 million Jewish-Poles and 1.9 million non-Jewish Poles).
Furthermore, historiography has moved away from talking about Slavs and Nazis in general, in favor of a more differentiated approach of talking about Poles and Soviets. One of the reason is the difficulty of definition that /u/marisacoulter details here and the second one is detailed by John Connely in his article Nazis and Slavs: From Racial Theory to Racist Practice. Central European History, Vol. 32, No. 1 (1999), pp. 1–33 which discusses that aside from general declarations of some party leaders, the category of "Slav" as an overarching idea for all speakers of Slavic languages did not play a role in the implementation of concrete policy in the occupied territories. Czechs, Poles, Russians, Serbs and so forth were viewed so distinctly different by the Nazis and treated distinctly different that the category of "Slav" is not a useful one in illuminating that history. It can not explain why Czechs and Slovaks were treated differently or why Croatia was turned into a satellite state and Serbia was occupied or why in Poland "carriers of Polish national sentiment" were murdered en masse while in Serbia they weren't to the same extent and degree.
All in all, there is a whole lot of vibrant, interesting and sometimes controversial conversation and exchange of ideas going on both among historians and also in the public of various countries (just take a look in Poland or Germany, where there is as of right now a public discussion going on about further extending the existing monument for the killed Polish citizens). The universalization of the experience that you within the contexts you are in, find this topic not sufficiently discussed is simply not based on the reality both of public discussions and historiography in many a different context. By broadening the wording in the way it is done above – "Why isn't this talked about more?" without any further context as to where it isn't talked about enough in your estimation – it comes off as complaining that Jews receive too much attention rather than an honest inquiry into the state of historiography and public debate.
Our resident expert on the nazis and the holocaust /u/commiespaceinvader has answered similar questions in the past
This one doesn’t really answer your question but he talks about the treatment of/attitudes toward Slavs by the nazis if you or anybody else want to know more in depth about it
Here he talks specifically why the focus is generally on the Jewish people (and Romani)when talking about the holocaust