It's time consuming & expensive to maintain, host websites and apps. From my experience that's the biggest reason most website eventually go down.

On Nostr Band, in their TOS, I remember they wrote that the website would remain free until they figured out a way to make money so they could pay for the hosting and more.

Recently the jelly fish relay said they quit because they couldn't make money to pay for the servers. It's not easy to make enough money to pay for sever costs especially since Nostr is still quite small in the amount of users.