By many less liberal lefties, porn is seen as inherently exploitative. The roots of the industry to this day are in some circumstances watered with human trafficking and barrels of cum misogyny, so it’s not a totally unreasonable position, it just is one more issue that is construed as black or white when in reality, the subject is far more nuanced.

Edit: Also many instances have no age verification and might be by local law obligated to block NSFW-content for their users.