Advertisers don't have infinite money. If Pornhub were to become as big as Youtube they would need a lot more advertisers, preferably big companies, to support both the website and the creators. And if they turn into a massive global platform, advertisers will care a lot more about what their brand is associated with.

Also ads have different values. An ad for a sketchy camgirl website pays a lot less than a Toyota ad. Toyota cares a lot more about their public image than a camgirl, and since a platform as big as youtube can't sustain itself with cheap ads, Pornhub will have to listen to the demands of big brands. So no matter which website you put in Youtube's position, they would be just as unfair as Youtube.