#1 in bronze but still stuck there. Why?
Just started playing SC2. Never played RTS before. It's been 3 and a half weeks since I'm number 1 in my bronze league (40 games won/ 41 games lost)-680 points.
What I don't understand is why I'm not moved to the next league?(silver). I'm not good enough or is there a bug?
Moving up or down in leagues is not as simple as reaching number 1, and then being pushed up to the next league (as is the case in lot of other games). If this were the case, anyone who played a lot (won a game every once in awhile) would be promoted rapidly thanks to their bonus pool, even if they weren't that good.
To move up leagues, you need to prove to Blizzard that you are consistently performing above your current league; beating a silver player once or twice will not suffice, you need to consistently win. As @Colin D pointed out, your current win/loss ratio is at 50%, which probably isn't persuasive enough to move you up to silver yet.
It is also worth noting that it is impossible to be sent down to a lower league mid season (Blizzard changed this very recently). Because of this, some people have been placed more conservatively, which might also make getting to silver tougher.
There is a lot more to it than that, and I encourage you to check out this post on TeamLiquid.net, which has a lot more explanation.