I'd argue it has less to do with the "capitalist systems" and more to do with how obnoxious "slugging" sounds. Commuting in your own car guarantees (a) you have a ride and (b) you have flexibility. You can change you plans, stop by the store, run errands, anything your heart desires (plus, not deal with strangers everyday. Ugh.)

This isn't a pro-car thing. I've haven't driven a car to work in 8 years (I pay out the ass to live downtown so that I'm close enough to walk / bike). It just seems like "Well, that sounds like a pain in the ass" is a simpler possible explanation to why slugging isn't popular in the US compared to Big Business not wanting it to be.