Actually that is likely not the case.   I understand your basic theory of Uber/Lyft are taking all the regular rides leaving traditional cabbies to pick up those who require disabilities.
What this doesn't take into consideration is that with whatever chunk of profit Uber/Lyft take, it eats that profit from cab companies.  Less profit, less drivers, less ride for folks with disabilities.
But the real issue is that if you offer a business it should be for everyone.   Hence why ALL stores have to offer ramp entrances for the disabled.   Uber and Lyft are skirting that and it is at the detriment to the civil liberties of those with disabilities.  It gets a tad sticky...