US cities pay too much for buses

Ultimately due to a lack of transit competition. Municipal transit will be bloated and inefficient on every level because no amount of failure will put them out of business. Indeed, most agencies' main goal is to increase budget (any increase in service or customer satisfaction is incidental) because more budget equals bigger projects and more staff which is more prestigious and higher paying.

I'm with you at heart, but experience says government owned transit works just fine and even great in other countries. What's their secret sauce?

Perception, maybe? My local transit agency seems to do pretty well. There will always be critics, but they don't seem unnecessarily bloated, the vehicles are well maintained and clean, etc. Not any different than a typical bus in, for example, UK. And I would caution that if you think everybody other than the US does government-owned transit very well, you may be focusing in a small subset of wealthy first world countries.

Other countries provide transit as a transportation service for all. US politicians and voters view it as a charity for the temporarily carless.

All the other issues are downstream of this mindset.

Historically denser cities.

I'm guessing that unlike here, some of those places need buses, and they simply can't afford any waste.