there's a place for them. say, the dog can't walk that far without getting tired, but enjoys the mental stimulation of leaving the house for a bit, and perhaps being taken to the park in it, that they would struggle to walk all the way to (not everyone can afford to run a car) and if they get pushed their, they get to have a little walk, a sniff around, see other dogs, etc. then get pushed home again.
you can't underestimate HOW much the mental stimulation fo a walk is just as important to a dog as the physical exercise.
this was always good for older dogs, and sadly, increasingly necessary for the inexplicably popular Brachycephalic breeds that often struggle to walk far without breathing issues.
I don't think people should breed dogs with such disabling deformities, but also, I know people that rescue such breeds, and the dogs still benefit from getting out and about, even if it's mostly watching the world go by from a pushchair, then a bit of a sniff about in a popular dog walking spot for the mental exercise.
and for the old dogs, it means they don't lose out just because they can't walk as far as they used to. again, not everyone has a car.
I've even thought about getting one for my cat, as he doesn't like to walk on a harness. However, he LOVES looking out of the window on car trips, and I think he'd enjoy getting to go out and about in a safe, secure carrier to see the sights and smell the smells without having to worry about cat-reactive dogs in the area or the fact that I can't walk far carrying him before my back seizes up (he's not fat or anything, I just have a lot of back and joint issues. I can enjoy a leisurely walk on a mostly flat route, and I think he'd love watching the world go by, like he does in the car.