I think part of it is that you are an "old guard" redditor. People coming from Reddit that have spent time there are going to recognize your username and follow you because of that. They may not necessarily have ever interacted with you on Reddit, but it's possible they've just read your name on, say, lists of former Reddit super/powerusers that aren't as active on Reddit any more (r/theoryofreddit and such have these sorts of "end of Reddit" posts quite commonly, I'm sure you're aware) and so they see you, maybe see your name suggested as someone to follow, and go for it. And remember, kleinbl00, it's not just what you post, it's also what you share.
That's all old-school shit, though. I doubt anybody remembers. Place has the memory of a cocker spaniel with ADHD.
To put it in perspective, I've been a casual redditor for a couple of years and when I saw your name I thought "isn't that guy from reddit?" and I've never had any type of specific experience with you.
It's good to follow people too, because it makes it convenient to check out their recent comments, even if you're not that interested in the stuff they post. Although I agree we need a better way. I have a lot more followers than some users who post way more frequently and more interesting material than I do. I'm not against your tag theory, but if people want to follow people, we should have a better way to find the ones that might interest them. We've tried tweaking the signup process, but clearly it's not working.
Agreed. BTW, twitter has the same problem, and provides a completely terrible solution by emailing me recommendations of people to follow, which I ignore with extreme prejudice. Though this may have to change as the site grows, I personally feel at this stage that the best path to quality recommendations for new users involves leveraging the 'badges' page.