It is, but 4chan is hardly the mainstream internet, and there's a lot worse than celebrity deepfakes on it. On Reddit, it has been relegated to a few pariah subreddits. Earlier, you would have spotted some on the homepage.
Not sure what you mean by "mainstream internet", it's a normal page anyone can access by typing its address into the browser. Well known, too. And if you're looking for this kind of thing it's the first suggestion you're going to find.
Sure, it's not on the most visited homepages of the world - but it hardly went away. Even on the most visited homepage it's just few clicks away.