Comment by notyourday

The problem with adult content is that it is not monetizable via regular ads. This means that Tumblr is either:

1) a porn site with porn ads which is not a sexy business to be in -- at best it is a lifestyle business.

2) a site providing tools to small porn businesses ( i.e. creators of adult content ) for money which has a very limited growth and is a tough market

3) a site charging users for access to edgy content

None of this so far has been a multi-billion dollar entreprise.