Can someone tell me why it should be hard to get as many minutes to your players as you want?
Because the training system is tied to weekly minutes played in a certain position. IMO it's an obvious game design choice that I find pretty difficult to argue. If one wants to change this, there need to be changes to the training system. These would not necessarily need to be major changes, though. For example a new tuning of the "how much training one gets for fewer than 48 weekly minutes" parameter just might be sufficient. One key point of course is that most people want to control the minutes to get best possible training. Remove (most of) that incentive and they are less likely to want extreme minutes anyway. Then give them that option.
IMO game design fails when people want to choose the extreme option (such as playing each guy 48 minutes a game in training position) and are rewarded for doing that. If that's easy and if that's a winning strategy at some level, is there anything fun and challenging in this aspect of the game anymore? Wouldn't the game be better off by removing that aspect and thus making it more simple and accessible? In this sense, the current system is actually pretty well balanced. Moreover, I think it's too easy to get 48 minutes and teams that field only 5 players are not punished enough. But that's just an opinion.