I agree with 1 but ppl already use free services (twitter) and willingly sacrifice their personal info and tolerate spam. 2 is charity. I support the programmers works but there is no real incentive for users to pay for relay services.

In Bitcoin node operators pay miners when they want to transact. They pay for access and security. They also help enforce consensus rules. This give btc value. Maybe relay operators should make it so you have to pay to post? Like 1 sat at first but maybe a market would develop for highly available relays? Or maybe you could stratify the network? Free later at the bottom and paid layers on top? To see top content you would have to pay?

The incentive I believe are:

1) As user base grows, spam may increase in feed or DM's. Joining and adding only paid relays may help prevent most of that.

2) You help keep the relays running to cover costs of running it and get access to content/events/notes shared by others without the hassle of setting one up yourself.