Leon didn't really have a place on this roster. The team is already going to hold on to Lynch, Turbin, Michael, RealRob, and possibly Ware at RB. That's 4 maybe 5 roster spots, and a 6th would be way too many. I view kick returners kind of like a closer in baseball. They're fairly valuable, and can win (or lose) you games, but for the most part they're not hard to find. Think about all the potential big play returners we already on the roster: Michael, Tate, Lane, Thurmond, etc.
The cutting of Leon was partly a cap issue, but mostly due to a lack of a roster spot IMO.