They don't

not any top club has strikers who track back to help out midfield. I don't mean they are stuck in the box, but what they ask in Italy is quite unique and retarded.
There are very, very few teams without Ronaldo/Messi that actually play 2 strikers (and even Barca could not defend Roma this year). One has always been Atletico and in their prime days they had Costa/Garcia who made the formation a 4-6-0, that's how defensive they were.
Otherwise if you are playing 4-4-2 and don't ask the strikers to defend, you are gambling big time that you can defend the other team with only 8 players. It's basically the difference between Juve-Madrid first leg and second leg. First leg it's 4-4-2 and MDS gets caught in midfield because we don't have the 5th player to take up the space. Boom 1-0, match over.
If Allegri was more defensive in the first leg, we could have the CL right now.
I don't know what changes from Higuain to Icardi. Maybe Icardi scores 3 or 4 more goals. But we will still struggle vs. teams like Spurs, going back and forth up and down the pitch, wide open, because we don't have enough players closing space.