I would say it is multiple different reasons. First, a good number of people can find some fault in some of her work. These faults are a trend across multiple works which cause people to notice them more often, which leads to a reduction in them enjoying those works as that is all they see. This als causes them to seek out more faults in other works, sometimes effectively imagining them there in order to further justify their dislike.
There are also other issues with her work, muscle development and the like. This, along with the other faults such as the dicks being off, causes people to think that she cant draw and make them angry.
It could also be the fans of her work, if she has a lot of fans, obviously she must have a lot of money coming in, right? Even without proof they will work off that focus. Even worse, as they attack her work, her fans retaliate which causes these people to further dislike her work and "rabid fanbase".
The last major concept I could think of is that they may actually be racist or sexist regarding this issue. Too many guys may dislike a female getting money for drawing a male figure. As they insist that she must never have seen a dick before, they are fixated on the narrative that she cant get a guy, but again they seemingly have no proof.
All this is of course conjecture. It is likely that any one person who dislikes her so much could have reasons in multiple, or even possibly none of the reasons mentioned. Unfortunately, the common user on 4chan still doesn't know about the Hide Thread option, and therefore we have to still listen to them.