[jewbacca]

Obviously not scientific, but if you need some totally informal causative bro-science to allow you to swallow these empirical results:

Even if the benefits are "obvious", the large majority of people aren't self-improvement-focused supermen with significant reserves of willpower at their disposal. Even the smallest increase in the necessary "activation energy" (comfort, expense, convenience; whatever) necessary for a task is going to put a large chunk of the distribution on the "fuck it, I'll just drive" side of things.

This is why "engagement" and "user experience" are multibillion dollar industries. Compare abstinence-only education, condom usage, and (kinda, if you squint a bit) drug prohibition.