There is a good post on socializing and not at Of Course I’ll Play It. Keep reading for the comments, which are also good. It starts in the context of social media games and addresses the age-old topic of forced grouping. I will not repeat what you can read there.
I want to group more than I do. A good group playing experience is far better than solo, but a bad group playing experience can be actively bad, not just worse than solo. Solo is reliable, subject only to the vagaries of the game itself. Solo is also low-investment. Putting a group together for X can take a long time, and it may never come together, and then I have the risk of its making my night worse than not playing at all.
Finding the right guild is a huge boon, because that gives you a reliable source of good group experiences. That is high investment, maybe less so for the extroverts. That is a better investment if you tend to play the same game for a long time or if you have a large, multi-game guild that will be consistently available in whatever game you play. (Of course, if the guild is that large, it may not be much different from a PUG with strangers.) Otherwise, you start fresh in a new game, trying to find a group that has the right social norms, has people in your level range/time zone, and is otherwise a good fit. There are many posts to be made on “finding the right guild for you.” I miss my City of Heroes supergroup, but we moved on in different directions over the years.