Then everybody will just defend like stuff until the cart is at the turning point then they knock the thing down and the cart has to move back and go the other way. More time wasted, less time left.
It would be pointless just to let them
destroy it instantly, again that video is only a
demonstration. It should take a larger amount of people and firepower to make a blockade.
Thought I also might let you know that, after it enters the intersection, the trap is disabled, they can't drop it any more.
The attacking team will also be able to reverse the effects of the blockade.