Most porn sites are owned by a single company. That company was exposed recently for inserting gay porn into non-gay porn searches/categories and also for saying it’s what 12 year olds want to see. This was done in a Project Veritas style undercover report by a conservative outlet so no one here is going to believe or care about any of it. It’s the same thing with the incest porn though. There is a concerted effort to shape people’s interests by exposing them to things they weren’t looking for. Could be simply to try to increase engagement and revenue or legitimate social programming who knows. Society in general is becoming increasingly open to taboos of all kinds and much of this is due to promotion via media.