1) Wheelchairs are being eliminated, slowly and systematically.
2) As they require repair, they are left to rot.
3) People use these free chairs in lieu of renting them at the parks, hence, no WDW revenue.
. . . you asked for a chair at the Front Desk
. . . you left a credit-card-imprint, in case the chair was not returned
. . . you had the chair for the length of your stay
. . . you could take it anywhere on property
4) Disney does not like giving away revenue.
NOTE: Resorts still have a chair-or-two. But, these are for emergency use or temporary use only. They are kept locked-up and they are not left with the guest.
I would disagree that it is an issue of revenue.
Disney doesn't actually rent the ones in the parks. They are provided by a contracted provider (I believe Scooterbug).
IMHO, the biggest 2 issues for Disney providing them at the resorts were all the hassle involved in doing it and liability in terms of making sure the equipment was in good condition and maintained. Plus, from what I understand, there was a lot of transporting a wheelchairs from one resort/back and forth to the parks as wheelchairs 'migrated' from the place they were provided.
Once they started the Featured Provider program, there was no reason to continue their own fleet of wheelchairs at each resort.
I think with only having one or 2 for emergency use, they are getting back to what it was originally.
Disney never advertised having wheelchairs to lend at the resorts. As far as I know, they were always meant for people who had unanticipated, urgent need for one.
I think the issue for Disney was that it became common knowledge that they had them available (mostly thru the Internet) and it became an expectation to get one for free. So, I think Disney accidentally got into a wheelchair 'business' that they never intended to be in.
Wheelchairs left about the resort already had a significant shortcoming, namely, none being around when you needed one. Trip reports have already mentioned needing a wheelchair to get from a park handicapped parking lot to the park entrance and not finding any.
So only a short hop, skip, and a jump to "eliminating" them.
It is possible to put together an hourly rental program for wheelchairs at resorts. Guests would have the choice (and probably much greater availability) of renting at the resort or arranging a rental from an outside firm. Or maybe the chair-or-two for emegency use already work that way.
I don't think Disney would ever put in place a short term hourly rental program. It would be a lot of hassle with very little benefit for them.
There is already a short term rental at Boardwalk (run by Buena Vista) and short term at Disney Springs (I believe run by Scooterbug). If they ever did an hourly/short term rental, I think it would be a contract service, done only at resorts, like Boardwalk, that get a significant number of day visitors.
Anyone who needs one for a short time at the resorts would also need one longer term (other then Boardwalk, which gets a lot of visitors to that general area). So, it makes more sense to refer those guests to one of the Featured Providers.