Felons don't have their voting rights removed because people don't like how they vote - they have them removed because the idea is that if you don't follow the law, you shouldn't be allowed to take part in making the laws. Voting rights are restricted for the mentally incompetent and non-citizens as well, for different reasons though.

If you look at the map, you see not a very strong correlation with the idea that Republicans remove voting rights from felons because they lean democrats(which I assume is what you were getting at). Literally only two states don't restrict felon voting rights, and that is Maine and and Vermont. If there was some voter suppression operating against Democratic leaning felons, one would assume states like California, New York, and Massachusetts would not restrict felon voting - but they do.