Nothing is free, servers must be paid. On top of that owners want to make money. We can enjoy free services while the investors money last, but in the end every long-term service must find a way to pay the bill.
(And some owners are more greedy than others)
It's the same with AI chatbots/API costs, heavily subsidized now and much more expensive in the future.
It's not like Imgur didn't finance with ads. They did that for a long time. Dunno if it paid the bills. The latest kerfuffle is because they were bought and the new owners fired all the moderators in favor of "AI moderation."