[chronial]

I think the idea is that you can have problems with walking that could be fixed by walking (I am currently in a situation like that after a knee surgery). I cases like that, this would not be a (objectively) helpful device.

But I do not consider myself qualified on this topic, as I have no idea how far the obesity problem has gone in the US.

[nommm-nommm]

If you have -limited- mobility then a device that can get you through everyday life instead of limiting your everyday life to your current mobility level is beneficial. Your hypothetical future mobility is not the point. If you can only walk 1 mile then this lets you get to something 2 miles away until you get to the point where you can walk those two miles. Working with an occupational therapist is obviously a complete therapy.

[TeMPOraL]

If you have problems with X that could be easily solved by Y, you don't buy device Z instead that makes problem X worse. People aren't that dumb. If they buy Z, they have some other reasons.

EDIT nevermind, I'm being stupid here. Too much coffee probably. Commenters below are right.

[jdbernard]

If Y is a strenuous activity (walking when very overweight), if the problems caused by X (obesity) are mostly long-term, and if Z is a device that offers immediate relief for X's short-term problems, then yes people very often buy Z.

People choose immediate gratification over long-term solutions all the time.

[chronial]

I myself just avoided walking for a few months, and I've seen quite a few people use aids that they should not use out of laziness. So I disagree with your statement.