Could it be that the "3 convictions and you are out" comes from trying to balance the fact that the system believes if someone is caught 3 times, they are likely to have done other times without being caught and that they will continue to do so for the foreseeable future (prison is not acting as a deterrent). Coupling that with the material and psychological impact on the victims, the system believes that society is better off having that person imprisoned for "close to life"?

If that is the case, society then needs to start looking at other incentives (carrot & stick) that can limit the risk of re-incidence, such as better reintegration mechanisms.