Part of the problem is that a lot of mass transit was built in the USA by private companies to make a profit. This went from trolley lines in small cities to large parts of the NYC Subway and almost all commuter and interciry rail.

Most mass transit systems ended up being built as loss leaders to develop suburban property. After the property was developed, the incentive to maintain mass transit dropped. Along with that, rail companies generally hated passenger service and preferred freight instead.

It eventually got to the point where the private company would collapse and there was little political will to maintain service. There was some lobbying done by auto companies, but a lot of it came from cities and states too cheap to make transit a public good with public funding.