why do people like to solo?

[Malrubius]

Because those who are grouping tend to be more anti-social than those who solo.

I like interacting with everyone, not just those who are talking to me in light-blue text.

DISCLAIMER: Yes, there are always exceptions. This is just a general tendency I've noticed over the years, and yes, when I'm grouped I also tend to be more anti-social towards those outside of my group. IMO, this is not a good or bad thing, it just is.