Muscle memory does play a role, but the enjoyment factor also kicks back into gear.
I feel like today many of us have forgotten that the discomfort of "hard work" is actually enjoyable. We get too much "pleasure" from passive activity, rather than finding active ways to grow.
I do miss being as active as I used to be because you do have much more energy through staying active. I used to ride a good 60 minutes every evening on an exercise bile until I blew up the motor and had it replaced with another model which was not the same experience. Will get my guys to swap it and get back on the bike.