well my response is two fold
first the planet probably gobbled up all the debris that was close by when it formed. second, planets move around in orbit just look at our own solar system, jupiter was once further away from the sun than it is now.. i'm thinking the planet was originally closer to its star, sucked up all the debris near it and has moved in orbit to a place where there is little further debris to be sucked up. in shorts its cleared everything near it, so that area of space is empty.