Uyghur language isn't banned in China, it's part of all the signs and official documentation. There are more Uyghur-Chinese documentations, dictionaries and references than in the West as explained in this document's preface. It is easier to practice Uyghur in China than in the West as again referenced in the document because there are less resources in the West or specifically the English-speaking world.
Should be noted that Uyghur is not descended off Old Uyghur but rather the Karluk languages. Yugur is the descendant of Old Uyghur.