People who begin cycling to work probably have a higher base level of health. Then cycling nearly everyday ends up being great exercise. The benefits of daily exercise are well known at this point.
Less than a hundred years ago you would have factories in city centres and people commuting there from within a walking distance.
Nowadays both environmental regulations and land prices pushed all that to the outskirts.
The last 30km along the expressway leading to my home city are lined with factories, logistics centres and whatnot and I'm sure most workers there commute by car.