[shiningdays]

I think the difference is in branding/positioning, and therefore the mental state of the person engaging with the site and creating content.

Porn = male gaze-y[1], intentionally and overtly about sexual gratification, less about exploration

A free-wheeling blog site = a place open to the exploration of a number of different aspects of identity, of which sexuality is one of them.

In short: If Pornhub were to create a tumblr clone, they'd inherently be enticing people to _produce porn_ rather than producing content which might happen to be somewhat pornographic. There's a huge mental barrier there for lots of people, even if they happen to enjoy viewing porn or producing sexually explicit imagery.

[1] Yes I know women watch porn, the default assumption of porn viewership is still a cis male audience