The ones I've added are from notes where people post things like "Check out this relay I've set up. Let me know if there are any issues."

Most of the 50 relays I have now were added by clients, as I have played with a lot of them.

I also added some when a client wiped my profile clean. I looked through a backup file I had downloaded before, and just started adding anything that started with WSS, and looked familiar.

My personal philosophy is that the user shouldn't have to mess with relays much. The basics of adding/removing should be simple. The more advanced stuff should be tucked away.

Amethyst makes relays ultra confusing. That's why I basically ignore relays. Feel free to look at the relays I use if you think you need to add more. You can login to Nostr using my npub to see what my feed is like, what relays I have, etc.