The fact that prisoners cannot have access to the internet is, to some extent, understandable by me. Filtering an inherently bi-directional communication perfectly, to make sure no information gets out is difficult.
But nonetheless, internet is not the only source of information in the world. The fact that people, who are in prison, are stripped, or seriously limited access to information, and thereby to learn, is really baffling.
If you find your resolution in the fact that you spent your time useful by learning, and when you reemerge and reintegrate yourself into society, you will have a chance to be better before, why restricting it?