This isn't true. Some people live in places where it's possible to reduce their driving quite a lot, but when they decide to do that, it isn't as easy as simply choosing not to drive. Once they're motivated, they start to figure out opportunities to drive less. They start to figure out which other forms of transit are practical in their area, and they figure them out one by one. They start to figure out how they can adjust their habits to reduce driving. (Fewer, larger trips to the grocery store, for example.)
There are a lot of degrees of "not driving." You might bike to work in perfect weather at one level of motivation, and bike to work in the rain at a different level of motivation. One level of motivation might prompt you to make fewer, larger trips to the grocery store; at another level of motivation, when you run out of milk unexpectedly, you might walk five blocks to a corner store of driving ten minutes to the supermarket.
The only perspective from which it seems like a clean either/or is for people who haven't yet found a reason to try. People living in the same neighborhood with the same economic means can and do drive drastically different amounts depending on how motivated they are.