Unfortunately, the effect wears off, and the second injection is a little less helpful, the third a little less than that, and so on. You can only give a limited number of steroid injections to a joint, after which you run the risk of actually killing off tissue and weakening bones. This certainly blocks pain, but does nothing for the underlying causes of chronic pain. It is a powerful narcotic. You can build up a tolerance to it and require a higher dosage for the painkilling effect.
People also experience a dulling effect on mental processes.
There is also a high risk of addiction.