From The Pavilion

Fatigue gives a general indication as to how tired a player is during the course of a season.
Playing matches will increase a player's fatigue. The type of match being played and the amount of effort expended by the player during the match affects the amount of fatigue a player experiences. For example, a player will experience more fatigue from playing a One Day match than a Twenty20, and a player who scores a century will experience more fatigue than one who is dismissed first ball.
Every day the fatigue of each player reduces. The amount of fatigue reduced depends on the age and endurance of a player. The younger a player is and the higher his endurance, the more fatigue reduces by.
Fatigue has a major effect on the performance of players in a match. Players with high fatigue will tire much earlier and their performance will drop markedly.
The fatigue of all players is reset to rested at the end of each season.
Note: A 'double fatigue update' occurs on Saturdays, with no fatigue update occurring on Sundays.

GM-crowfan65 wrote: ↑

Sun Jan 19, 2020 11:02 pm

Fatigue gives a general indication as to how tired a player is during the course of a season.
Playing matches will increase a player's fatigue. The type of match being played and the amount of effort expended by the player during the match affects the amount of fatigue a player experiences. For example, a player will experience more fatigue from playing a One Day match than a Twenty20, and a player who scores a century will experience more fatigue than one who is dismissed first ball.
Every day the fatigue of each player reduces. The amount of fatigue reduced depends on the age and endurance of a player. The younger a player is and the higher his endurance, the more fatigue reduces by.
Fatigue has a major effect on the performance of players in a match. Players with high fatigue will tire much earlier and their performance will drop markedly.
The fatigue of all players is reset to rested at the end of each season.
Note: A 'double fatigue update' occurs on Saturdays, with no fatigue update occurring on Sundays.

That is the basics from the rules
Friendlies do not add to fatigue and in general a player will take 3-4 days to recover from a match
The case with your players is simple they are playing 3 times a week, 3 x 3-4 = 9-12 and there is only 7 days in a week
Without going through all your matches I assume this has occurred for 3 weeks and that explains why your players are heavily fatigued.
Best thing to do know is play the most rested players and put the ones who are fatigued on rest trng as they will recover 1 full level that way.
It will help that you are now out of the MKMC as well


Also note: players with worse than moderate fatigue receive less than the full trng also