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A reminder in the age of the Fediverse: if you're not the customer, you're still the product.
(slrpnk.net)
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.
At the moment it's probably still paid by donations and by the people hosting it, but like any site, it may need to be monetized to keep going, or even just if its owners decide to. It's not like there's any guarantee of privacy just because it's in the fediverse.