If it was up to the teams they could have just went with any game at any time against anyone they want and that would work for them, but since it's now all decided, they are facing teams that UEFA tells them and they play on the dates that UEFA tells them, which is limiting.
But it doesn't take the League of Nations for that to happen. This has always been the case, all matches of the national teams are carried out according to the FIFA calendar and continental associations. Even friendly matches are held on dates defined by FIFA, in this case what differs is the choice of opponent that is made by UEFA. It should be noted that all over the world national teams played games, friendly or not, on the same days as the Nations League games.
from all aspects of the match and the match schedule itself has not changed where UEFA is setting a match schedule in accordance with the FIFA calendar where there is no domestic competition in several European leagues only FIFA changes the format and tournaments to be more competitive than last season's matches, a move that taken by UEFA is very good by making some matches more interesting so that it is no longer entitled friendly match but rather a tournament held in general even though the UEFA Nations League tournament is not as prestigious as the world cup matches or other competitions