Why Borderlands 2 Level Cap is Still 50
 

Are you wondering why the level cap is still 50 in Borderlands 2? Well, aside from Gearbox "not planning very well," you can blame consoles for holding back PCs again. That's by design. Some of those things start to become game-breaking. This has actually created a huge problem for us. We designed the skills really well this time, but we did, for better or for worse, make a lot of the decisions with the knowledge that there will be no more skill points available to put into any trees after you reach level 50. We knew the impossible configurations. Some of the design exploits that. Some of the impossible configurations, if they were possible, would break the game. Sometimes very literally. "Oh, that's gonna blow memory. Your Xbox will crash."

http://www.hardocp.com/news/2013/02/..._cap_still_50/