They're compelling and useful largely because of enormous public investment in supporting infrastructure. Without gigantic roads they'd be much less appealing.

Depends how you define "voluntarily", but it does appear some developed countries have slightly lower kms-traveled-by-private-vehicle per citizen now than they did 10 or 20 years ago (e.g. there was a study done in the UK in 2012 showing a 4% drop since the late 90s). It'd be good to find some more recent and easily accessible references.