I agree with a lot of what you're saying, but you are arguing that fame is the only thing that matters, while I'm trying to assert that both fame and the phenomenon I am describing matters.
There's tons of better looking and more entertaining girls that have attempted to stream and things like that. Many reached a base level of popularity or occasionally went viral. Enough to have started the jump onto the hype cycle.
Many of these girls should have easily maintained their popularity if fame was the only thing that mattered, but you'll find most don't.
Part of the reason why this is the case is because of the phenomenon I'm talking about. Some girls are 'stickier' given the userbase, and build a more consistent group of loyal simps. Girls like Emiru, Amouranth, and Pokimane basically succeed in being slightly attractive but still mid enough that the typical twitch user finds them appealing/'in their range', while objectively hotter girls didn't get the same number of consistent simps since they are more intimidating/'out of their league'. You need a base level of 'stickyness' to even have a chance of becoming famous in the first place.
If fame was the only thing that mattered, at least 1 or 2 out of all the popular girl streamers would be objectively hot just based on randomness, but you'll find literally none are, instead they all are pretty mediocre.
edit. how 'sticky' do you think these girls would be if they were open about having boyfriends while they were building up their 'core following' stage for example