A) Cars have a tall stack of interest groups with money to throw around politically. Manufacturers, Dealerships, Gas corporations. lobbying groups including, especially, but not limited to the AAA all have skin in the game and have thrown money at politics. (In general bicycle groups are rarely as organized, rarely have much in the way of profits or income to burn on political favors.)
B) Taxes. Today roads are partly paid for with gas taxes and sometimes vehicle property taxes. A lot of motorists feel so entitled to the roads simply because they see those tax numbers directly on their gas bills and vehicle registration fees and think that they own the roads because they feel like they have the receipts. (Nevermind that there is no state in the US that entirely pays for roads out of such taxes, and the "I paid for it, so I own it" fallacy seems to refuse to ever actually prorate its "ownership" against the actual small percentages any individual contributes to the total budget.)
Which is hilarious because road damage squares with the weight of the vehicle and bike lanes would need to be repaved maybe once per century.
If you replace 3 car lanes with n cars/lane/hour by 2 car lanes plus a bicycle lane, car traffic/lane/hour goes down as soon as you have over n cyclists/hour on that bike lane. At that density, that bike lane looks empty (https://www.boredpanda.com/space-required-to-transport-60-pe...)
I think that is massively underselling the disruption to traffic. Depending on the city and the traffic patterns, hundreds of thousands or even millions of people could be commuting into a city on a given day. Reducing the car throughput on a significant portion of roads will cause backups to spread across the road network, affecting thousands.
Maybe switching to bike lanes can be a net positive, but it all depends on the commuting patterns of people living and working the city. Then again, maybe if car commuting is made painful enough, it will accelerate shifts in commuting patterns.
With careful planning the interests of vehicle commuters and cyclists can be balanced for maximum benefit, but I think in the long term changing zoning and development strategies will be what's needed to really make the shift.
That said, it still depends on commuting patterns, road topography, etc. Some cities have a majority of workers driving in from distances that would be impractical for most people to bike. Making a big shift to bike lanes without making other changes to reroute and accommodate traffic would just cause gridlock and frustration for most.
If shifting city centers to being bike centric is done on a longer timeline then capital improvements and redevelopment can be done to support it in a way that makes it more efficient for everyone. Some cities can do that on a shorter timeline based on current constraints, others would take longer. Ultimately I think it's the right direction to go in.
You can maintain throughput and accommodate even more people on bikes if they just ride on the streets themselves rather than confining them in narrow bike lanes. A general purpose traffic lane can accommodate far more bikes than any bike lanes possibly could.
Hint: I don't drive, I walk.
It is not about forcing others, it is about freedom of choice. Bycicle is just one of the modes of transportation. People without choice have to use car.
Personally, I think subways should be the backbone of every city transportation system. But surprisingly even very environmentally conscious cities choose to forgo subway systems.
And your answer is 0... How? Bridges and tunnels between buildings? People evolving to fly?
Every person would require door to door taxi — tremendous increase in traffic. Same with bike lanes, take them away from Amsterdam and city would choke. Every Amsterdam driver benefits from less cars on the road.