I know I'm too cynical for my socks but I'd say it's: Money.
Despite the fact that you can so easily gain customer 'brownie' points by doing this right and attract a whole family because they know the one person will be well cared for?
Also, this service cannot easily be fully allocated to others - there will be some central overhead. Accountants don't like central overheads that cannot be neatly palmed off. (Just a guess based on 34 years experience in the grown up world.
)
My mother is now too frail to travel by air any longer but I do recall the fine service she got at IOM and LHR in the 1990s, early 2000s. When I met her at, and then put her on, a flight at JNB (2002) the wheelchair assistance was tip-top. It was also good at LCY in about 2006.
I do hope you get them
ExXB.