Because at the top of the server are the old known issues.
-The same opponents again and again, everyone is known to others
-other managers don't care much about their teams but they can set the right formation and orders, have the full training and win bonus and let their games in auto.
The more you involve, the more you loose
-difference in quality doesn't matter much
-you may promote or let you in the same lv cause there are not enough opponents
So if you still like the game, I think starting a new team from the beginning is a more interesting challenge.