A reminder in the age of the Fediverse: if you're not the customer, you're still the product.
OP was taking about Tumblr, but I think it applies even more to the Fediverse: users need to develop an ethos of paying to support the sites they use. Otherwise advertisers pay the bills and call the shots.
Passion projects still cost bandwidth, if not hosting fees.
Also, major news and media sites are not going anywhere. Little passion project sites will not replace a platform like YouTube. Serving video is expensive.