What is the real reason that Dalai Lama banned the practicing of Dorje Shugden is unknown.
Actually it's very well known.
The mix of Gelugpa and Nyingma teachings is deemed by the Dalai as essential, in order to provide the necessary religious and ritualistic support to his theocratic Gelugpa-Nyingma “rime” alliance.
Since Dorje Shugden is the protector of the pure Gelugpa teachings, he and his practitioners became the obvious target of both the Dalaites, and their allies, the power hungry Nyingmapas.
And, since the Dalai-Nyingma sinister alliance is also the Western bet to intrude, divide and plunder Tibet, it also follows that the practice of Dorje Shugden is hostilized and labeled as a “dangerous cult” by Western or pro-Western press, mercenary academics, and so forth.
I always believed the truth will be reveal when the ban leave.
It's precisely the other way round: the ban will be lifted when the truth is revealed, or when enough people realize that the emperor has no clothes.
Then we will all say farewell to both the ban and to the naked emperor, who will rotten forever in the garbage bin of history, together with his colleagues, Western puppets such as Pinochet, Reza Pahlavi, Mubarak and so forth.