cars are like 98% of the traffic or more

They didn’t always. That infrastructure was built and subsidized so they were used.

Purely from a safety standpoint, outright prohibiting bicycle traffic on motorized roads would be a massive improvement at the expense of inconveniencing a small minority of people

Purely from safety standpoint, making less motorized roads would be a massive improvement and people would conform to new modes of travel just like when cars and interstates were introduced.