Earlier quoted context omitted.
Those problems don't plague most other metros of the same vintage (e.g. Berlin, Paris, Moscow, St Petersburg, Tokyo, Osaka...) even though homeless people and vomit are prevalent there too. I don't know why NYC and BART have to have those issues.
Because half the American population supports a party that thinks public spending should be banned. So you end up with the classic 'privatise the profits, socialise the costs' setup. I don't understand why people can't see that some public spending is an economic force multiplier. I mean US infrastructure is notoriously bad for a developed economy, you have thousands of bridges that need massive remedial work to make…
The reasons behind this poor efficiency are complex and no one really knows how to fix it.
Here is an interesting article on the NYC Subway System. It's obviously about one small slice of US infrastructure but the general story is the same.
https://www.nytimes.com/2017/11/18/nyregion/new-york-subway-...
A lack of spending is not the problem.
Also, incidentally, since you mentioned "privatise the profits", it's worth noting that the Stockholm subway system is operated by MTR Corporation, a for-profit corporation based on Hong Kong.