The issue is not just the physical condition, this can be more or less well managed by the players and technical teams. The issue is the preparation time for the tournament. The technical teams of the national teams will have less time to prepare the team for the tournament. The internship period will be shorter.
with the increasing number of test matches or other matches of course it is used to understand each other,
that's enough and again the role of the coach is also important to unite them
For the national team, they can play well and the players can understand each other, they don't have to spend a lot of time together. As you said,
it is quite routine to do friendly matches, it will create good teamwork. Moreover, fellow players will also easily communicate because they have
the same language when they play for the national team. The process of cooperation between players is also much faster, therefore every time
there is an international event, the preparation is not too long. On the other hand, I agree that the cohesiveness of a team depends on how
the coach approaches the players so that they want to work well together. Especially big players who are already popular are more difficult
to control, here it takes a coach who can be firm with his players. And also actually players must also maintain their attitude if they have
strengthened the national team, because they carry the name of their country, so each player must eliminate their ego for the success of the team.