It'll give us more cap space.
Front loading cap hits doesn't mean much. It's the guarantees and signing bonus that lock down a team to a player.
Cooper gets 20mil on average, but his deal is a 2+1+1+1 by the way of a low signing bonus and guaranteed base that runs out by 2022. Cowboys could easily move on from Cooper in 2 years with 16mil in cap savings and only 6 mil dead if cut in 2022. His cap hits are 12mil and 22 mil this and the following season. He takes home 40million over those two years. With his 2022 base becoming guaranteed I assume in case of injury due to his 60 mil of total guarantees if injured.
His contract is "backloaded".
It's always smarter to backload the cap hits. Higher cap ceilings in the future + less guaranteed and smaller prorated signing bonus leftover money in the future means the team gains the advantage over most players. They can simply move on, restructure or extend, lowering the cap hit at the later date. Or, if the player is declining ask him to take a paycut or be cut.
With cap space being able to be pushed forward into following years, you take the saved cap space now.
If it was an use it or lose it, then front loading makes more sense.