Simplex runs on a network of relays, as does Nostr.
Eventually those Simplex relays will need some incentives to keep running. Nostr has multiple ways of handling that.
Why bother having two networks of relays when you can just have one? nostr:note1h7rg5gdzz60ux93csk38du06wgt9s0uaxz69ln7c663myjua53ysuvgaev