When I have tracks that don't loop, I loop them myself. That can take hours of fiddling with the track in music player software to get the sound to continue so the player doesn't notice.
My levels can be anything from 2.5 minutes to 15 minutes long, depending on the game. One track is unlikely to cover the entire level, so I need the track to loop.
If a track stops and there's a pause before the next one starts, it breaks the player's concentration. They suddenly become aware of the change, and it could hamper the game play - especially if they're playing against a clock.
If I use multiple tracks on the same level, I need to blend them. But here the problem is to find tracks that are similar enough to sound like a continuation of the same song, but not identical, so there's variation. If there's an unexpected change in tone or speed, it could also interfere with the game play.
I can understand that a boss fight level could use its own track that is odd. But I write casual games, I don't have boss fights in my game.