The 3 things you're missing are:

1) How uncomfortable lower end chairs can be for their users

2) How many of the little design decisions in lower end chairs can add up to a lot of pain

3) The chairs you buy online are almost exclusively all made in China using Chinese labor and pricing, where as the one in the linked article is made in the US paying US wages

But I want to talk about 1 and 2 for a moment. My spouse has developed a need for a wheel chair from time to time, so we originally bought a cheap one, just like many of the ones listed there. Specifically we bought one of these Drive chairs for about $140 (https://www.amazon.com/gp/product/B008KMKVEK/).

Among the small "papercuts" of using this thing:

* It was extremely uncomfortable after an hour or so. Bringing extra cushions and padding was a must

* The bearings were pretty awful and there was quite a bit of rolling resistance

* After enough times being transported folded up in a trunk, the plastic wheels deformed enough that one side rubbed on the frame every rotation. Not enough to make it unusable, but enough to add even more rolling resistance, in addition to requiring constant adjustments to keep going straight

* Misc bolts and pieces on the frame would catch and lock with each other making un-folding or folding the chair unexpectedly complex at random times

* 41 lbs is a LOT of extra weight to be rolling around with just your arms when you're already trying to roll yourself along.

* There was so much slop in the frame, rolling over any uneven surfaces was an exercise in frustration at best. Everything moved and shifted and your balance was all over as things twisted and buckled under any surface that was a completely flat linoleum hospital floor. In fact the thing that finally did the chair in was a trip to a park where we needed to be rolling over the grass and roots and dirt. A twist too far going over a rough patch of ground broke some of the pieces that hold everything together.

It was a perfectly serviceable chair for an occasional need that lasted us about 4 years of light duty use (some of which was during COVID, so very light duty in some cases). And when we replaced it, we never even considered buying the same one. It wasn't worth the money saved. It's hard to really describe, but all the little pain points made it so that in many ways the chair felt more limiting than the medical condition itself. And we were and are extremely fortunate that we're still able to decide on a case by case basis whether to use or not use the chair. If it was something we had to use every day, all day, I would wager by the end of the first month we would have been looking for something else, and it might have lasted a whole year before breaking.