I'm working on a blog post on this now. Unfortunately I understand this piece a lot less. If you point me at a market and say "build a product for this market", I'm pretty confident I could do that and be the best. But if you asked me to pick a great market, I'm not confident that I could do a great job at all.
I think finding and analyzing market opportunities is much, much harder than building great products. There are hundreds (thousands?) of phenomenal product managers, but only a handful of people that really understand markets. The few that come to mind are Marc Andreessen, Peter Thiel, Elon Musk, Jeff Bezos, and Steve Jobs (unfortunately he's gone now). I've read all I could find from them, but even they are having trouble articulating this, which suggests they don't have it entirely pinned down.
I'll see if the blog post goes anywhere in the process of writing it. I'd really like to understand this better.