I had a similar realization. My inner desire had weird bits of fear and narcissism at its core. When that side of me cracked the desire to perform vanished. I did do some math after that (mostly to asses brain damage after health issues): i could do some new stuff, and did enjoy it.. but something changed, there need to be solid reasons: either aesthetical (a sudden epiphany that I need to study topology) or social for me to go into workhorse mode.

Another thing is that I also realized that crushing is not progressing.. so very often I understood things without any effort, what it took is for my brain to accept an idea more than anything else.. so I stopped forcing things, I simply walk around ideas and let things come and go.

All in all.. I also believe that is simply biology talking.. when young all you care is being the best, with age your focus spreads over other people (SO, kids, family)