Yes, it is difficult to get Tibet visas for Tibetans who are not Chinese citizen. Many Tibetans want to visit their home but they can't obtain Tibet visas. The only reason is that they are Tibetans, no matter your a person on Chinese black list, or a ordinery person. As long as you are a Tibetans, the chance to get Tibet visa is rare.
However, we found a way to get Tibetan visas for Tibetans who are non-Chinese citizens. You need to pay to relevant Chinese officials and find the right person to do so.