Same here. When I had braces, I got them on only my lower teeth at first. I got braces on my upper teeth a few months later. That wasn't at all unusual at the time.
An friend of mine got braces on only her lower teeth about 20 years ago. She actually needed braces on her upper teeth as well, and that's what her orthodontist wanted to do, but she only wanted her lower teeth straightened.
As for the original question, I've seen a few people with braces only on their upper teeth, but not many. Maybe it was early on in their treatment and the lower braces were soon to follow ??