A system of mirrors prevents a single node going down from taking the whole system (in theory at least, we've all seen plenty of times where failover goes poorly), but it doesn't do anything to ensure the long term survival of the system as people lose interest, lose the ability to participate, and sometimes die.

If you were around certain internet forums in the late '00s you might have run in to an image hosting platform called WaffleImages which was created in response to yet another popular free image hosting service locking down their embedding and ruining thousands of old posts. The goal was to distribute image hosting among community-operated mirrors, and it worked great for a few years. Over time though people lost interest while the rate of new mirrors getting added dropped to basically zero and eventually it fell apart.