Cause you can't actually GO anywhere on a bike. If you want to go somewhere 200 miles away for a week, it'd take a day and a half each way, minimum, and you can't bring anything with you bigger than a backpack. It's also physically strenuous to go literally anywhere, even the places you are allowed to go.
cities should look like this: bicycle/walking paths, trains, trams and buses. and a tiny road for the rare occasion you actually NEED a car. boom, problems solved. also mixed use zoning, rezone every city so it's more compatible with a non car centric lifestyle