I always roll my eyes a little bit when managers complain that their players are playing too many games. As
@millossobek shows, they should be happy they aren't coaching in South America!
Footballers now are only playing slightly more competitive matches than before, mainly because of the addition of the Nations League — which has replaced international friendlies (you could argue that they have the same effect, given that many national team managers routinely play the same core of players, competition or not), for the most part. Those FIFA international windows remain the same as they were, competition or not, so their players are going away for 10 days in Sept/Oct/Nov/March. You can argue whether or not it's necessary, but it's not necessarily
more than before.
Plus, only the very top players are playing more than 45 matches a year. The average bottom-half player in the Premier League is playing less than 45 games, including cup competitions, on a weekly basis and nothing during international breaks.
Managers and clubs have a say here — they are generally poor at keeping their squad fresh and giving players that need rest a break, because...results. Clubs are also pretty poor at building squads (Football Manager AI isn't that far off when you look at how Manchester United and Chelsea do business). They also don't need to take weeks-long summer tours of America, Australia and Asia, which aren't conducive at all to season preparation.
And the clubs could probably reject money-grabbing moves like Champions League expansion and the Club World Cup. And anytime they suggest something like ditching a League Cup, it's met with outrage from the lower-division clubs that rely on that gate money...