In the Mohave Wasteland though... isn't really much of a wasteland. Animals are plentiful, including lot of relatively peaceful ones like brahmin and bighorners. Even geckos, coyote and giant ants are in plentiful supply in some places. Even more importantly, people have ranches and farms dotted all over the place. Even places like Goodsprings everyone has little gardens to tend. So the presence, even abundance of strange meat is.. well, strange.
Just because you think cannibalism is taboo, not everyone believes this. In fact, there are tribes to this day that continue to partake in cannibalism. Some people prefer human flesh to any other meat. It may not be something you want to accept as it so ghastly, but it is what it is.
In the Capital Wasteland, the Family had alternatives, but they craved human flesh. By only drinking the blood of people (via Blood Packs) they were able to hold off their craving in order to keep from being ostracized by the rest of the Wasteland.
Some people just LOVE human meat.....plain and simple.