That's because (1) Pornhub was named as a defendant along with Mindgeek / Aylo in the Girls-Do-Porn lawsuits concerning human trafficking. (2) Most of the members there who upload videos go unverified. There's literally thousands of unverified members over there. (3) Pornhub has taken down hundreds of thousands of videos because those unverified members also do not own those films. It borders on close to half to three quarters of a million in video clips. (4) No pictures are allowed to be posted as well. Those were all taken down. Members, who at one time uploaded pictures, had them removed by Pornhub as well for the same issue, the G-D-P incident. Pornhub members don't own the pictures. The websites they took those pictures and videos from own the rights to them.
Xhamster went the same route because of the lawsuits that Pornhub / Mindgeek went through. Xhamster wasn't named as a defendant. They dropped all pictures. And videos need to now have the website watermark on them. If they don't have the watermark then some form of the watermark needs to appear during the viewing of the clip. If they don't, they get taken down. As for Xvideos? Well they are always targeted with cease and desist letters by content owners and webmasters. It's common practice to see videos that were once up get deleted / taken down over there at xvideos.
If you want a video or photo gallery, become a member of the actual website or network or join adultempire, hotmovies or elegant angel. They will usually have it.