On that game bejeweled 2 deluxe how come some rounds last longer then others?

Is it the moves i make or what?? how come one game will last 3 rounds and another will last 9?


and how come it says round over when there's no timer and more moves to be made still??


thanks|||because you either have diff time amouts for each lvl





or because you hadent reached the qualifications like a certain number of points gained required for that lvl