In a blowout game, neither team learns much from it and few players get better during them. In a competitive game, players are forced to play their best because they are playing against kids with similar skills. They might hone learned skills or develop new ones, but they usually always get better, even if that “better” is the result of a failed play, botched technique or a mental error.
In a lopsided win, good coaches don’t run up the score. They put the subs in, run basic plays, and do things they wouldn’t do in a close game. If the team is losing by a lot, the same thing usually happens. By the end of the game, not much has been learned on either sideline, by the coaches or the players.
In a close game, coaches put players into situations that they know they’ll need to be able to perform in with success during big games, like the playoffs. In blowouts, even if you run the exact same play, the execution, or not, of it is against either much higher- or lower-skilled players. So, the coaching staff really doesn’t learn if their players will be able to handle the same situation in the pressure of a close game.