Because it is super easy to damage the truck by using M3/WC51, or even Rifles, if the damage carry to the HQ buildings it won't even withstand a few mortar shots, which is totally retarded.
Also, his SC2 drone example is absolutely wrong. Drone with 1 HP will morph into a full HP pool.
Ahh, I see a simple solution. If you're scared of that happening, don't push squads with the truck.
Sounds like the risk you take to me.
As I haven't really encountered the push much, I don't see it as a huge issue. However it seems logical that if you were "totally retarded" with your truck, you deserve a damaged building.