Point is they are plentiful - I can hail a cab in minutes but if they become rare I could wait 30 minutes for the 'special' cab to show up.
If they become rare, wouldn't the market supply more cabs? I mean, how do you think food supply works?
I think you are the one who doesn't understand how food supply works. Stores stock items which are popular - not ones which sell rarely. If disabled passengers are less than 5% of all taxi passengers, private companies might ignore them entirely because they are not worth the investment into their fleet.
"The free market will fix it" has historically not been an effective answer to problems the disabled have.
Yes, but then you have to subsidize them. There are also advantages to cabs not needing subsidies.