I'll try to explain. The first rule of life that you have to understand it's that life isn't fair. People without disabilities can go to conferences and expand their social network better than quadriplegics. They can go to more job interviews easier. They appear to have more options than disabled people. They appear more dominant and able to negotiate a better salary.

A potential employer wants to pay the lowest salary for the best work. They think (and based on what you wrote, rightly so) that they can get away with paying quadriplegic people less.