I honestly think it's good to at least offer a possibility to go to raids and dungeons without needing a guild. People who really want to get "better" at it will end up in a guild anyways for coordination reasons (among many, many other reasons).
Also, guilds don't serve a mechanical function only, they are also spaces to socialize, know people and share experiences. So I don't think no one "needs" to be in a guild, but that is not necessarily bad, there are still many reasons for "wanting" to be in one.