Especially with contract work, it's very limiting for a person with a disability. If you have a base income support that you're surviving on, and you can go back to work but it's a contract position, you're not sure what's going to happen after that. It's a disincentive to take that job.
A lot of the time, if you leave, especially if you have an insurance program, it's hard to get back to the income level you were at before. With a contract, maybe you're not provided with insurance within that company to provide for your medical needs. Then you're not getting all the benefits you would need as well to support your disability. It's really a disincentive for you to go to work.
It's true that the programs have to change so that they encourage people to get out and work and then accept you back in if that position fails. You need a safety net there in order for people to pursue employment.