Tumblr's founder is strongly involved in the product decisions there. Prior to the Yahoo! acquisition... there were still a ton of head-scratchers in product, marketing, and operations over there. Staffing rumors indicated the young founder built a very close team on the executive side & had a number of sympathetic early investors on the ownership side.

These are not inherently evil people, but they were allowed to impose terrible, deep mistakes on the staff and users for a very long time. No one was in a position to stop the unforced errors, not for years. Which is why Yahoo! was a fitting acquirer. (The sale to Yahoo! probably prevented the platform from foundering)

The core product is still extremely useful to the web (especially because it's free). The demand for such services, and a capital market that rewards any kind of operation as long as it's acquiring ~u s e r s i n t h e d e m o~ - it gives a very long runway to digital publishers like these.

But 9-10 years is a long time to be around without a stable business model. And, as a very worrisome problem, you would not be able to persist your user data or your established URLs if the platform foundered. A shutdown of Tumblr would be a terrible single-day source of Internet linkrot.

But, same for Flickr, which is a much more admirable (and longer-lasting) product run by capable people but faces the same existential threat. Sad, because Flickr should have been Facebook (eventually).