This is such an easy subject that I’m certain that I’m not the only one who knows why Moscow's subway looks like a museum and the NYC subway a literal toilet.
There was a time when American subways were impressive. I’ll concentrate on NYC because that’s the one I have personal experience with. Here is a picture of an abandoned subway station and an example of what a subway car used to look like:


If you’ve seen the footage of Tucker Carlson touring the Moscow subway station and comparing it to pretty much every station in NYC, you know which one you’d choose to use if forced.
Why is there a difference? And why does the NYC subway system currently look and smell like what you would expect in a third-world country? It’s simple: those subways were built and maintained by people with an identity. Their collective culture and consciousness allow them to maintain it and not deface it.
Compare that to a city consisting of many cultures in a society where radical individualism is pushed and you get random homeless people shooting up, people pissing out in the open, and literal rape happening on a crowded subway car where no one intervenes. Now is the time someone will find an article about an assault on the Moscow subway, which will be them making my point by providing one exception. Granted, the exception doesn’t always prove the rule, but most of the time it does.
Americans have been and are subjected to a multi-cultural society that was sold as a melting pot but is really a salad. Combine that with a spirit of radical individualism that has been pushed upon this culture from the beginning but significantly exploited after World War II, and you’re going to suffer the “tragedy of the commons” in places where multi-culturalism and radical individualism fester. The United States as a whole does not possess a culture; localities do. And even those locations are beginning to crumble. We either choose to build culture where we are or are in danger of even more remote places embracing the spirit of the current NYC subway system. We must either start building or choose to gate-keep because it’s coming for us.
We could have nice subways by making strict laws and enforcing them. This is a great argument for order and doing what must be done to have order.
People will behave if you use a big enough stick. Like a singapore cane. Even animals can be made to understand consequences.
A shit salad at that.