The game is designed so that, if you get promoted every season, your players just fall short of keeping up with that progress. It's frustrating but not enough for you to get annoyed, you just have to replenish the squad every year.
How do Nordeus want you to do that?
Yep, spend a few £/$ whatever every season.
The trick is to not get promoted every year and you can quite happily bring on Academy players and keep them for 6,7 even 8 seasons, as well as a Scout or so every year with your tokens.
You always have plenty of red and green packs this way as well and it's a rather more realistic way of playing as storming up the leagues year after year buying tokens may well make you fall foul of UEFA's new Financial Fair Play rules!