They are routinely equated. Reputable sources, including Wikipedia, will list them both as some of the major historical genocides or crimes against humanity. You'll learn something like this if you take most history classes that study the period in university. Most of what you're referring to seems to come from certain political/nationalistic elements or those that see it as justified in a utilitarian way by the importance of the US in 'creating' the modern world. And it doesn't help that calling attention to it has come to be associated with left-leaning ideology and academia, which means that people on the other side are naturally going to respond skeptically and dismissively.

The Holocaust is unique in having a high PR impact. Remember that it was not the first attempt at deliberate genocide in history. It was particularly shocking because the victims were a relatable part of Euro-American culture, not Africans or Armenians or East Asians who could be treated as an "other", being persecuted by one of the most sophisticated and advanced standard bearers of the Western world. It confronted the whole idea of "progress." This created a kind of revulsion that hadn't been felt for crimes of the Soviets, Japanese, or earlier Americans. It occupies a particular spot in our historical consciousness which makes it hard to make a comparison.