I've read the following questions regarding what factors influence a player to move between leagues:
- When exactly do players move between leagues?
- Starcraft 2 - Hidden vs. Visible Ranking
- Starcraft II - Are you stuck in a league once you are placed?
- many more...
However, I've been browsing through StraCraft 2 Rankings and have noticed a few players that have 2,000+ points, a good w/l ratio, and play regularly but are in bronze or silver league. Some of these players are even #1 in their league. Why haven't these players been promoted?