This is because inter Milan has refused to bring in younger players to strengthen their squad and this has impacted negatively on the and we saw that in the finals of the Euefa champions League finals were they were humiliated by PSG, inter Milan should start a rebuilding stage if they are to come back to competitive football challenging for titles.
Italian clubs recent years no longer have good finance and they can not compete with rich clubs from Premier League, La Liga and even PSG in Ligue 1 for buying star players. They have all changed development strategy with initiatives to maximize contributions from loan players, free players while they try to find young and cheap players for their clubs. This strategy can work or fail but in general, it's not sustainable and Italian clubs must spend more resources on their youth academies in order to have sustainable good home-grown player supply.
In the Club World Cup final, Chelsea won against PSG with young players, and PSG defeated Inter Milan with young players, meaning that if you want to improve the team's performance, you must rely on young players. Yes, the team needs experienced players, but a young player can perform as well as an older player, but he cannot perform like that young player. Inter Milan must get out of this misconception and recruit talented young players to the club and develop them in their own way. If you build a team like this, you will see that Inter Milan has become a strong team again and this regret of losing in the final is gone.
I can not understand your point here as I see both PSG and Chelsea have quite young squads that can be their bright future in next 5 to 10 seasons. Inter Milan are different than PSG and Chelsea with many old players and high average age in their squad, so they will have to renew their squad this season and next several ones. Inter Milan actually have come to very last seasons as peak of this player squad and if they don't plan well for squad restructure, they will have big troubles and get declining performances soon.