Let's look at the reasons for the ban and you will know why:
1.The Dalai Lama identifies Dorje Shugden as a "spirit", and claims that the tradition of propitiation associated with Shugden elevates this spirit to being equal or superior to the Buddha. He states that encouraging the worship of Dorje Shugden could contribute to reducing Tibetan Buddhism to a form of superstitious spirit worship.
2.The Dalai Lama states that there is an "acknowledged link" between worship of Dorje Shugden and sectarianism between the various Tibetan Buddhist schools. The Dalai Lama believes non-sectarianism is "his most important commitment", and that the worship of Dorje Shugden may be a barrier to this commitment to non-sectarianism.
3.The Dalai Lama says that Dorje Shugden has a long history of antagonistic attitude to the Dalai Lamas and the Tibetan Government they have headed since the time of the 5th Dalai Lama. He identifies the 5th and 13th Dalai Lamas as having specifically spoken out against Dorje Shugden as a threat "to the welfare of beings in general and the Tibetan government headed by the Dalai Lamas in particular". He states that in light of the current difficult situation endured by the Tibetan people, it is particularly important to resist the worship of Dorje Shugden as a potentially divisive practice.
If a serious ban is imposed, and these were the petty reasons given (in blue) and yet not explained well with proof, they sounded more like accusation or hear-say. How can China negotiate with the Dalai Lama or the people who impose this ban?
Also, accusations (in red) that Shugden practice may be a barrier to non-sectarianism- while it is obviously practised in Sakya and Kagyu as well, and that it is a potentially divisive practice- although Shugden was considered area protector for some areas, these are creating more negative circumstances and obstacles to arise.
In Praise of the protector Dorje Shugden composed by the great Sakyapa master Kunkhyen Ngawang Kunga Lodroe,
For entire Tibet, included in upper region Ngari, central region Ue-tsang, and lower region Dokham,
you act as the very protector, refuge, supporter, and friend of all people without exception,
thus you are the very god of the snow-land country, I prostrate to you.