Question

Why doesn't the earth grow bigger

Answer 1

1) majority of the 'dust' in the solar system has already been accreted millions, if not billions, of years ago by the planets and sun. There isn't a heck of a lot of loose matter left out there 2) Any planet with an atmosphere will burn up any non-gaseous matter 3) technically speaking, the other large bodies without atmosphere ARE still growing. But you'd probably have to wait hundreds of millions of year for that growth to even happen. Generally speaking EVEN though Earth does capture those space 'dust' things (about 40,000 metric tons of it each year),it's still to little to be noticed.

Answer 2

Earth is basically from matter, all the matter around the Universe came together to form Earth, the only way for Earth to grow much bigger is if there was an unlimited supply of matter, there isn't and therefore Earth cannot get much bigger than it is now.