so... in the end... I've understood where I was playing wrong.
(rushing first turns...)
Yes, you got it.
In the "first" runs (like 20 or more, I'm a stupidly stubborn person) I was trying to "win" the first rounds as soon as possible, theoretically to have more turns in the late stages.
I started winning the game, spending every turn that I had, and closing on the last turn, cleaning the deck and buying more powerful cards.
I think I had won one of the games having started with not more than 4 or 5 turns.