Why do you think people who rush/minmax don't have fun?

Everytime I see this rhetoric being pushed it makes me roll my eyes. Lots of comments and posts seem to assume people who rush content and minmax gear that will be replaced soon are miserable. But maybe they do it because it's fun for them?

I think most of us have limited time to play due to jobs and such, so why is pulling half a heroic dungeon and nuking it down seen as a bad thing and not the ""proper way""?