Actually the Italian population is 59 millions, not 40, there is a big difference. Anyway immigration just to have more available football players is one of the most ridiculous things I've ever heard. You get good football players having a clear project, having infrastructures, training facilities, good coaches, etc etc. Based on what I read here it simply looks like that a country needs more people, then explain why China and India are so bad that they can't even find 11 good players with more than 1 billion people each...
I will give you a very simple statistic.
In 1990, the population of 15-25 age group in Italy was close to 10 million. According to the census, as of 2025 this has declined to around 4-5 million. Total population keeps on growing. But the player pool is getting reduced.
Now compare the situation with Uzbekistan, who recently qualified to the world cup. In 1990, they had 2 million people in the 15-25 age group. As of 2025, this has increased to 6 million.
What I am trying to say is that demographics will have an impact. The argument with China/India is not suitable, because in these countries football is not very popular.
Of course demographics have an impact because it reduces the amount of youngster that may eventually choose to pursuit a football career but that can't be a reason (or excuse) to open the border to more immigrants. Otherwise how come small countries with very little immigration like Croatia and Uruguay are so good and they only have a few million citizens?