I would too. But that doesn't mean you can't take up a hobby that is done alone but shared with a club. I got into car work and joined my local auto club. We do meets, drives, and grab beers every once in a while and share experiences or things we've done. EDIT: Not to mention the social point of "I fucked up, who knows what they're doing and wants to share a case and fix this mess"

I've been hired by a few friends-of-friends to build automation and although the coding and electrical is done at my little workstation there's a local maker group that I like to share my works with.

I always recommend picking up a hobby that has tangible products. Gaming and Reading are all mind exercises. Doing something with your hands helps work the body and when you've worked at something for long enough its much more visual for how you've honed your craft. Its a different type of reward than coding is. I don't know if I can describe the feeling it gives but it's different somehow, and it's a good feeling to look down upon a physical creation with pride.

Hiking IS a group activity. There's countless hiking clubs on Meetup.com. They frequently seem to serve as singles mixers in fact.

Music is also a group activity. Have you never heard of a "band" (or "garage band")?

There's also cooking clubs on Meetup.com.

What exactly is your idea of a hobby that involves other people?

Or rephrased, you're doing it wrong if those three normally group activity examples don't involve other people and you're an extrovert looking for relationships.

Unless, of course, you don't particularly like having to be around other people.

Hiking by yourself is glorious.