I agree that people often miss the easy answers on sleep. It's important, though, that light/dark and exercise are not interchangeable sleep aids. Very, very broadly:

Light issues are about melatonin, which is production-inhibited and rapidly destroyed in the presence of blue light. Increasing melatonin levels is the point of Flux and blue glasses and all the rest.

Exercise issues are about adenosine, which is produced over time and gradually with physical activity, and consumed during sleep. (It's also what caffeine inhibits.)

These aren't entirely interchangeable, so there's more to be gained from addressing whichever one is the largest personal issue. (Anecdotally, I have a suspicion that the feeling zombie-tired insomnia is about a bad mismatch from sedentary tiredness.)

I do think that people preferentially worry about light issues without trying exercise, though.