I’ll take this further, whilst car volume undoubtedly plays a prominent part, it’s driving attitudes that ultimately determine how many people cycle.
The UK suffers poorly on both fronts, especially with the latter, hence many people who want to cycle understandably conclude it’s not safe to do so.
Bicycling is an inherently safe activity. Cars make it unsafe, scary, and nerve-wracking and that's what prevents many people from riding. It's pretty simple!