So couldn't the game "recognise" active players from lower levels and offer an incentive for them to level up more than one level to help fill higher levels with active teams.
Something along the lines of: Congratulations manager you've won your league so we would like to offer you the opportunity to rise 3 levels. If you choose to accept the new challenge we'll give you 150 tokens, 500 million dollars and 150 rest packs to help you on your way at your new higher level. Oh and your current squad won't lose a star this season!!!
Ok, some managers won't want to lose out on the possibility of trophies by jumping levels. But there will be others who would accept the challenge of going up more than 1 level if the incentives were there. No?