Because it's long, stupidly difficult, and doesn't fit at all with the game's premise. This is supposed to be guerrilla warfare, and now I'm taking on a never-ending (really, they respawn infinitely) army by myself with a single fking tank. And then I have to get out of it and run through 20+ heavily armed troops with no cover to get to the objective. Which is a ****ing tank that I now have to kill ON FOOT, again with no cover, and the ammo box doesn't supply me the rockets I need to do it. Blowing a bunch of **** up with a rapid-fire rocket launching tank is only fun so many times.