This is a dishonest answer. Tumblr died because it’s niche was adult content. Banning your niche is choosing to fail.

It doesn't seem dishonest to me; chasing those ad dollars are what led to the supremely stupid decision of banning one of their core niches.

We are talking about platforms where the ads themselves caused users to leave. This is not what happened with Tumblr and it is not a good faith view to say so.

I only see you attempting to constrain the topic that far, rather than just the ways that advertising based models in general can pervert a company's incentives by turning away their core user base. Sometimes it's just changing the UX until your userbase no longer wants to show up. Sometimes it's literally just banning a huge chunk of your userbase for some reason.

it's a good thing Marissa Mayer came in to buy Tumblr as a strategic acquisition for Yahoo! for 1 Billion dollars (after Tumblr imploded).