>>15457703>>15457446It's because he escapes before it actually stops, there are cuts of the clip where you don't see it stop.
The whole thing was a work, Seth was supposed to move out of the way, and they were always going to stop it with enough room for him to do so. Look at Seth's left leg and hip, he's glued to the mat, he's in now way trying to actually get into the ring. He is instead laying as flat as possible to make sure he doesn't swing up into the spike and working like he's going to get in. It's hard to explain, but because of physics he's only in danger if the cage is dropped onto him, not if he bumps into the stationary spike. The cage's weight is supported by the mechanism dropping it, if it comes down on top of Seth, suddenly he's bearing the weight not the mechanism and he's getting gored. If he bumps up into it, however, he can't overcome gravity so the hardest he can hit the spike is the power of his body swinging up. Even if the cage is still moving downward, it's only a problem if Seth actually gets pinched or doesn't move out of the way when it hits his back.
Top 5 WWE stunt in the past decade.