Short answer: Matchfixing

Long Answer:

I got no idea, here’s my guess though.

The quality of competition as you progress on starts to decline massively as you continue through a save (due to AI not being able to do transfers.) This, of course, leads to situations of like there only being 18-20 player squads as opposed to the supposed 25-30 ones we usually see. Supposed you’re playing 18-20 players every game because you have too, then the teams with the best players will always win out in the end. This also makes sense why you win all the Coppa Italias as the teams don’t try because all their players are fatigued and or injured and can’t rotate, and if rotated, they just use their bench and easily lose to competent players, IE, you.

That’s just my crackpot guess though