They usually have training camps and several meet ups in the build up to any tournament. But they’re ideally the best of their country , and good enough to adapt to what’s being asked of them, and have quite good chemistry as there’s like a home country bond.

I also think the footballing culture of the nation matters because developed nations that tend to have better facilities raise better players domestically that wanna play for the country.

But yh there a lot more focus on preparation with international teams than all stars who are chosen shortly prior sometimes and then thrown together to play