Originally, Damus and Astral (at least) chose to share relay configuration data in the unused contents of kind-3 contact lists, but didn't write a NIP.
Quite a while later NIP-65 showed up for advertising to other clients where you post your shit, so other clients can find your shit (and to a lesser extent, where you pick up shit people want to send you, the "inbox").
These are not the same thing, although they are clearly related. The data I need to configure my client's relays is quite a lot more than the data I want to tell other people about where I post. In fact, I want to lie a little bit.... I post to a relay to archive my stuff, but I don't want other people pulling from that fragile little relay.
Damus doesn't support NIP-65, gossip doesn't support saving to kind-3 content relay lists, some clients use NIP-65 for both purposes, and other clients are all over the map. So nostr is broken, and while we now have a clear direction for how to find other people's relays, we still don't have one for how to share relay configuration data between clients.
There is a proposal to usekind 30002 as a relay list for configuring your client, so things are still changing: https://github.com/nostr-protocol/nips/pull/786