Many subway systems are profitable, like the Tokyo JR East. If there is a will there is a way. Americans simply prefer sprawl and cars when it comes down to it.
The vast majority are not, the systems in a bunch of Asian cities (mostly in Japan, HK, Taiwan, Singapore) are the exception due to a few reasons, most notably because they use distance-based fares and land around stations often belongs to the operator bringing in massive commercial revenues.
It's impossible to know if Americans genuinely prefer sprawl because the alternative of building more compact communities is banned by regulation all over.
