This is a common misunderstanding about warhammer fan content, they don't just take down anything that involves their stuff, they've never taken down peoples stuff, generally if they think your stuff is good enough, they hire you on for their own content, this is what happened with Helsreach guy, and this is what happened with the Astartes guy, both of which now work for Gamesworkshop and make new animations under them. People reference Emperor's Text to Speech as an example, but they never told him to take it down, he cancelled his show on his own and moved onto a different project, his material, Helsreach and Astartes are all still fully available to the public on youtube still and many other people have since made warhammer fan content and are still left up as well.
People heavily assume they are, but they really aren't more so than any other company, i mean every single videogame ever made about warhammer has been a third party creation, and 70% of their lore has been fan written or started as headcanon, Warhammer exists as a sandbox in the first place for people to kitbash and create their own stuff, all the way since first edition. That's not even going into things like Warcraft and Warmachine and the vast VAST list of miniature websites that produce their own third party warhammer minis like Kromlech.