Probably related to the increased prevalence of remote work. It's much easier to walk to lunch or to run an errand when you're working in a downtown office block, less so when you're working from home.
Gee, it sure would be nice if people's homes were within walking distance of errands and restaurants. Oh well, no use dwelling on something we all know to be impossible!
America's horror show of urban design is definitely a big part of it, but the proliferation of delivery apps since covid has made it that a lot of people don't even need to bother leaving their homes to do errands anymore. For a class of people, there's really no need to walk for any reason other than leisure.
The first part seems to be major, though - the steps from and to your parked car are not nothing, but if that's your primary mode of transport, they don't really add up to much
