Well - every content is to some people irrelevant. The groups just differ.
Leveling is relevant for people starting their first character, or questing through different zones, or on different faction than before. Sometimes, your race or class play a role. It's not relevant anymore as soon as you have your Loremaster. Old raids are relevant if you have not done them at all, or if you still farm collectible things like transmog and mounts. As soon as you are done, this content becomes irrelevant for you. And then there are people who have started in the lastest expansion and could not care less about MC and BWL and are completely fine with skipping it. They should not be forced to run this content, because its clearly outdated and they will probably not learn anything for the current game (because balancing is completely different now).