Actually, the one year contracts are generally correct. That's because they're either arbitration eligible or renewable. They're still under team control. If you go through the off-season, you'll see there are different times to deal with each group.
There is no license to get for the minor league players. We're able to have actual major leaguers because of the license with the MLBPA. There is no equivalent for minor leaguers, so SCEA would have to negotiate with each and every single player (which obviously is quite a prohibitive task).