Busses get tiny subsides in the US.
It’s a large percentage of total bus revenue by design, and a significant expense for some local governments. But the number only look large because of how we split the vast majority of government spending into federal and state budgets with local budgets being relatively anemic by comparison.
Buses are implicitly subsidized by road maintenance spending. Road wear and tear occurs according to the fourth power of axle weight, which effectively means almost all of the wear and tear is incurred by the heaviest vehicles, which include buses.
The farebox recovery ratio in the US is awful. Most cities are somewhere between 5-25% of operating expenses coming from fares.
Perhaps the tiny subsidies (in absolute terms) are because the bus systems are just so small?
SFMTA's farebox recovery is around 25%. London Underground is about 130%. Osaka Subway is 209%.
https://en.wikipedia.org/wiki/Farebox_recovery_ratio