The reason is quite simple, if the team from series A is more believed that older players are more professional and have great experience in all competitions and certainly have a great mentality. Not that only relying on old players, but some teams have also begun to rely on young players who are currently in the process of building the expertise possessed by the young player.
And on the one hand when comparing EPL with series A, in my opinion it makes no difference. Because these two leagues are equally competitive and in fact there is no dominance and Inter becomes a strong candidate in UCL a few seasons ago when qualifying for the final round.
I would guess that it's also a bit of a cultural thing where they just did that for so long that they think that is the way everything works. Don't get me wrong all of these players grow up somewhere, which means that not like they do not have any good young players, they of course have some good players and that works, but I think it's clear that we are going to end up with a situation that will not be all that simple.
We could consider the fact that it is going to end up with some good results, this is why I think it is important to realize that we are going to have some issues, and we are going to face some trouble with it, and that's why we need to consider how dangerous that could be, and how young players need experience as well.
With the logic of "veterans could help us more with their experience", you will not have any young players who will grow up to have experience, meaning that if there are veterans right now, that means they played somewhere when they were young too. All in all, it is an Italian thing, it's more like a Serie A thing even, where they like using older players on their club and get that veteran leadership and do a lot better with time, should be important in that case.