I would guess this to be short term. If they are truly in the business of game management then they must have a surplus of deer that need to be taken care of. Allowing muzzle loader could be one way of keeping deer populations lower. But of course when such populations become to a safer level the use of muzzle loader will have to be once again restricted so the population doesn't grow too small.
Unless they really don't care about game management and they are just trying to sell more leases. But considering the DNR has signed off on it I don't think this is the case.