StarCraft 2 - why haven't certain players been promoted to higher leagues?

It is possible to reach an unlimited value of points and still remain in bronze league. Blizzard's ranking system will randomly 'test' you when it feels you might be ready to move up to a different league. It will put you against a player from the next league and check to see if your 'ready' to move up. To answer your existing question, these players are winning against players they are expected to win against, but losing against players in the next league.

Blizzard views this as a perfect balance. As long as they continue to win, they will continue to gain more points. But as long as the continue to lose their 'test' matches they will remain in that league. Keep in mind that being 1st in a division doesn't mean you need to be in a different league, someone has to be in first.

Both of these team liquid threads give some great information about SC2 ladder and how to move between leagues

SC2 Ladder Analysis: What YOU Need to Know

SC2 Ladder Analysis: Part 2

Hope these help