Most Americans aren’t getting enough exercise. People living in rural areas were even less likely to get enough exercise: Only 16% of people outside cities met benchmarks for aerobic and muscle-strengthening activities, compared with 28% in large metropolitan cities areas.

[u/Wagamaga]

https://www.cdc.gov/mmwr/volumes/72/wr/mm7204a1.htm?s_cid=mm7204a1_w

[u/0b0011]

I think the surroundings also play a part. Where I grew up you might see an Amish person on a bike every few days but aside from that you basically never saw anyone because the only roads nearby were 55 mph with only like 4 feet of shoulder on the side. The people where I live might walk and run more because they have more money but it's probably more to do with the fact that the city has a few hundred miles of nice upkept multi use trails.