This isn't true at all, Blaze was a huge success, scrolling through Tumblr you see people with silly numbers of checks, lots of people pay to remove ads, it's just that that the successes aren't massively revenue generating in the way that ads are.

Trying to monetize user generated content is hard because both the users and creators believe that it's their content (which it is that's how community works) and so locking it away and taking a non-trivial cut is going to be met with insane vitriol and there's not much value to add over the base experience. Tumblr's patron thing you should of think like Hashicorp re-licensing Terraform.

And worse is that sometimes creating true value-adds naturally perverts incentives. Like for example a true value-add would be "bubble-as-a-service" because Tumblr has some really nasty subcultures which is why posters don't like when posts "break containment." It would be the easiest money ever to just pay and get a huge blocklist without having to go through the effort of making one yourself but then you kinda need those nasty communities to justify the value.