It's not just the size of the playerbase. I'd happily group if it didn't mean I'd end up at high rank with skills that just aren't developed enough, and are hard to practice at high rank.

Put another way, when I'm trying to spam up skills, I already gain experience too fast. Grouping would make that worse.

What would be good is if you could toggle the group exp bonus into a learning bonus. Then I'd be grouping whenever asked.