Why are prisoners not hired

According to the laws of every country, when a person is taken to prison in order to achieve the four aims of the criminal justice system:

Punishment
deterrence
rehabilitation
protection (of society from further acts)

the courts then decide what is the appropriate number of years the criminal deserves to be held behind bars in order to meet the aims I have stated above.
After being released, often as part of their requirements is to find a job. Unfortunately one of the question asked is whether or not a person has served time in prison, and more often than not, it becomes the basis for their rejection.
If government is putting so much funds in keeping these people locked up for years on end, feeding and clothing them, why do they not put a bit more funding to making sure that they are able to find jobs, because if they are able to accomplish the rehabilitation process, then they should be able to work well. If however, these former criminals are unable to find employment, they get desperate for work, or food, end end up resorting to their old ways, which takes them back a step, and makes it easy for them to go back to jail. The rehabilitation process would have worked, but only for a limited period of time, due to the harsh environment of the outside world.

We should therefore consider helping out these people, because it is also our job to assist in deterring them from their lives of crime. If they become unemployable, then they resort to other means, which we all do not want.