What's the drive or motivation behind people running syncthing discovery & relay servers?

Do they generally then run their own clients to only use their own servers?

With Tor I'm convinced over the "speech should be free, I'm making the world a better place" type argument.

With syncthing I'm incredibly impressed that this optional (but incredibly useful) infrastructure is being run by people for free since it doesn't quite make the world a better place in the same way? It just saves a bunch of other people setting up their own relay/discovery server on a cheap linode/aws instance?

Impressed!