Star Wars: The Force Awakens... More of a gripe than a question. spoilers within?

**SPOILER** like it matters. what a pos

At the end when that one chick light speeds her ship into the First Order’s main ship and completely destroys it…

Why the hell isn’t that a weapon? You have robots. You have light speed on every ship, big or small. Seems pretty effective. I’d be willing to bet that if you stuck a light speed drive on a big rock you could destroy a planet with it. Apparently the Death Star was never necessary.