Too much international football. All the politicians read that shit book some years back claiming that football helped solve regional politics and world peace, and football was quickly expanded into a never-ending political wankfest.
I love the game of football, but it's absolutely used a bread and circuses type ploy to help distract and soothe/quell local populations.
Anyways players these days cannot handle so many games. Squads need to be expanded, and rotation used more heavily. Old-school managers that don't believe in aggressive rotation as now failing as they don't have enough healthy players to last these longer campaigns. At least the Prem expanded the number of subs that can be used, and you could see, most progressive managers make use of all of them EVERY game.