It's because US cities are poorly planned, crumbling shit-holes with 4 lane highways criss crossing them. People are extremely hostile to bikers in most US cities, and there are literally no consequences to killing them much of the time.

American cities are so unpleasant to exist in on the ground level people prefer the safety of their smog machines at all times, even if you are going half a mile down the road for a carton of milk.

Everything is designed to funnel you out of the city into your extremely inefficient suburb so you can stop by taco-bell and wal-mart on your 50 minute commute home.

But hey, the answer is more roads right? Not incentivizing people to have less roads on the highway?