In principle I see it, and I did used to have this opinion when I was younger. But as I’ve got older I’ve associated getting paid with working (for some odd reason) and the last thing I want to do is work on my relaxing evening jog, and think about how much money I can make.
I would love it if an employer would let you take time off during the day to workout, though. There’s only so much you can work until a lunch break