I think you're right. I run basically the same route every time (varying distances a bit), through a county park that's literally down the same sidewalk where I live. I also listen to the same six or seven songs, changing a few of them every month or two. Most people who know this is my routine think this must be unimaginably boring.

But within a couple minutes, I don't even notice, and I'm just letting my mind drift, sometimes to the extent that I've overshot my turnaround spot by more than a mile just from a lack paying attention

Having experienced this, I can't imagine now going back to the "old way" where I have random songs that differ every time, or different routes that require me to pay attention.

I've often thought the repetitive nature of the same route and the same music actually encourages the metal drift.

Hmm, interesting point about listening to the same songs every time. I used to have youtube on shuffle as my go-to work music, but eventually a bad song would come on and snap me out of concentration. I found that a few songs and albums worked well for me, and I could just leave them on repeat. "See you again" by Wiz Khalifa and Charlie Puth is the one I feel weirdest about. It's so cheesy and poppy, and I'll listen to it for hours at a time.