There are two reasons:
one：
Due to the lack of heavy tanks in China. The WZ111 is the only self-produced heavy tank, and although it is only 60% complete, it is still eligible to appear in the game. But it should be on the non-tech tree. If it appears in the form of activities, then China has no other alternative heavy tanks of the same type. Many gamers can’t get it once they miss it. So it should appear in the game as a gift pack or Golden Eagle like American T58/Soviet IS-6/French Soma SM, so that everyone has a chance to get it.
Two：
The WZ111 is closer to the Soviet T10 series and should be weighted around 8.0. If you put it behind M48A1 on the technology tree, it will become IS2 (heavy)-M48A1 (medium)-WZ111 (heavy) on the technology tree. In this case, the technology tree will be very chaotic.