The rural population isn’t the issue, it’s suburbia which is where the majority of the US population lives.
It’s not dense enough for public transportation to be viable and it’s zoned in a way that makes pedestrian traffic a non starter.
Suburbia causes a lot of problems. I understand why it exists - owning a house with a yard is nice. I personally wouldn’t want to give that up to live in an urban environment if I didn’t have to
And on the flip side of things, I live in Florida and biking as a primary method of transportation in the summer is just insane.
I do bike for exercise in the summer and 15 minutes will leave me drenched in sweat needing a shower.