Walking is simply not an alternative for moderate distance with a bike. For example, Google Maps's biking time for a common route near me (train station to university) is 6 minutes. Walking time is 26 minutes. The distance is 2km, so that's 20km/hr biking or about 4km/hr walking. I've tested this with longer distances and it seems to hold. In my experience, Google's biking speed is fairly spot on for me, and its walking speed is a bit faster than I walk. So I'd imagine that biking is at least six times faster than walking for me personally.

Also, if I really have somewhere to be, I can bike substantially faster and be OK, but running for half an hour with a heavy backpack and bags is much harder.

I spend a decent amount of time getting around on a bike - an hour and a half yesterday, maybe a half an hour today, so just the last two days alone I'd have spent twelve hours walking! That's totally unacceptable.

Finally, I imagine that biking (although easier) isn't that much less healthy than walking. Still much healthier than driving.

Walking BEST. Biking, second best. If too far, too hot, too steep, e-bikes third best.

Plus good public transportation.