I am a healthy adult and I'm also continually enraged at the state of sidewalks in my area. When I walk my dog there are some routes I simply cannot take because the sidewalk just... ends. I think some lots extend all of the way to the street and it's up to the property owner to put in sidewalks and many simply don't. If I walk across their lawn to get to the next private sidewalk I get yelled at for messing up the grass that they spend "so much time and money" maintaining; fine, it's your property and I'll stay off, but what a waste of resources. Unless it's a particularly quiet road, I shouldn't have to walk in the street. The city-maintained sidewalks that do exist are a travesty: no curb cuts as you noted, tree roots that create huge steps, holes, and some have no curbs so people just drive on the sidewalk. The city doesn't want to do anything about it because these are either privately "maintained" and they can't, or it costs money and they don't want to.

I do think that mobility scooters should come in off-road versions because I've never seen one. I don't see why $3000 can't buy something closer to an electric ATV with knobbly tires, full suspension, and a torquey motor that can mount curbs like a boss, but it's a chair format and is limited to fast-walking speeds so that it isn't a car. It's probably a low-volume issue.