It's not that I don't want to support relay runners, but I don't yet understand what it is I'm missing out on 😅 probably just because I need to do more research. I just don't have the time 🥵
Discussion
A big part of it is spam management. Paid relays are better for that.
Another is quality of users/content. Typically low quality people (harassers, racists, the annoying and senseless, etc.) don't want to pay for services so their poor content/thoughts ride for free while better stuff plays on the paid relays.
I'm sure there are other reasons, but those are the two I joined nostr.wine for.