There is clients that "work" the old way, with the dev havin no spare resources for this, so they won't fix it. For the sake of a good standard, clients should not support old standards but users will blame the clients that don't find their relays for being buggy, so client devs will add this interoperability.

Yesterday or so I saw there's a project that documents what client doesn't play well with another client. This kind on project can give the users a perspective on who's at fault here.

Maybe we will have tools to upgrade profiles so clients can just implement the current nips and not care about legacy support across all of them.