Reading between the lines, Popular Mechanics believes that China cannot anticipate where the burn up and re-entry will take place. The thinking goes that most controlled descents are planned to take place over the ocean, where there's little to no risk of harming people. An uncontrolled descent means that any debris that survives re-entry could strike a populated area, and if you've seen Armageddon, you know what that means.
At least Tiangong-1 has made its home nation proud up to this point, since it was only designed to operate for two years. It actually wound up being in operational orbit for 1,630 days -- more than twice the planned duration. Wu Ping, deputy director of China's manned space engineering office said that the station had "comprehensively fulfilled its historical mission." Let's just hope that all the components get turned into ash before they reach the ground.