I actually have an answer to this. lol.
Game devs are divided up into teams. And they specialize in each section of the game. So say people that work on the presentation won't work on hockey puck physics and collisions. And on top of that some bugs are harder to fix than others and fixing one bug (passing perhaps) could have a huge ripple effect and completely disrupt gameplay. Other fixes could just be as simple as editing a database number, but sometimes a bug may be hard coded in and require extensive manpower and hours to correct.