As hackers we are driven by our insatiable curiosity. For me at least this curiosity is not often applied in the same direction.
Being a polymath doesn't mean you find lots of topics interesting, it means you significantly influence multiple very broad and diverse fields of knowledge. You write papers on nanotechnology, cured cancer, wrote, starred in and directed a blockbuster movie.
You also overvalue the term hacker. I can't tell you how many people I meet who think they are a hacker because they can get a Drupal site up and running or write a blog. I had a boss one time who was so happy that he had finally gotten back into coding. I said, "What'd you do?" He said, "I changed the HTML on the login form!" Ugh.
So, "hacker" is not synonymous with polymath. Hacking is just one small field of knowledge that may be a part of a polymath's repertoire.
polymath: a person of wide-ranging knowledge or learning.
Wikipedia says
In less formal terms, a polymath (or polymathic person) may simply refer to someone who is very knowledgeable.
I feel like that compulsion to dive head-first into something is a feeling that hackers and polymaths must share.
I also didn't mean to imply that I was a polymath. I don't even really consider myself a "monomath". I am still very much a student.
How many "hackers" here are accomplished authors -- not technical books, but social subjects or good fiction -- and accomplished programmers, and have accomplished something notable in another unrelated field?