>I thought horses was banned because they ... produce some unwanted mass on the road which hard to clean?
>
>Cars on the other hand, don't do that at all.
Cars do it, but instead of it being a hard to clean mass, it's a nearly-impossible-to-clean toxic gas that kills thousands of people every year.
Non-electric cars will be banned in most inner cities probably within the decade because of their pollution, sort of a parallel with how horses were banned earlier.
It was already addressed in other content that they're not banned everywhere, but additionally, the poop you mention is not a big problem. In many places horses in the cities are forced to wear horse-size napies which catch the poop.
Cars do it, but instead of it being a hard to clean mass, it's a nearly-impossible-to-clean toxic gas that kills thousands of people every year.