that's cause it ISN'T. There is nothing any MORE ridiculous between a hero in a wheel chair then there is a hero that gets hit by a giant's axe 3 times (including something we call a critical hit) and they can keep going like it's nothing.
If you don't understand that people in wheelchairs have very little they can't do, and we have a fraction of the abilities magic gives you.
It certainly doesn't seem a hard thing to handwave in a lot of the typical fantasy worlds - especially if it makes a player happy.
Given it's high tech/magic (swims, jumps, climbs vertical walls, etc...), is it valuable? (But how often do thieves target the party for other valuables, and as far as "gear" isn't so and so's noble background valuable?) Are they commonly available to others who might benefit from it or is this special and only works for this one user? (How many people who would need one for mobility did the party run into before this character?) Does it fold if they come to a tunnel (how would a Goliath get through?) or for like riding in a wagon or boat (where is the Paladin's warhorse?). Are all the doors wide enough (did anyone worry about door width until this came up)? Does it allow full speed in standard woodland settings? (Do you have wagons get hung up on things if the party has one?). Does it have unlimited climbing ability to the point the thief would like to borrow it (does the Paladin have unlimited climb in his plate mail?). Why isn't this magic/tech used for all kinds of other things? (See threads on how magic in D&D doesn't always seem like it makes much sense as far as how it impacts society).
But I can certainly see someone taking a few minutes to process the handwaving the first time it comes up - especially if they are really into versimilitude outside of the usual D&Disms. Maybe this should be in the PHB as one of those D&Disms?