My guess is that they closed shop knowing that their chances of repeating such a remarkable win were too slim to warrant the exorbintant costs associated with operating a Busch team. They pulled off one of the biggest wins ever, in a field full of veteran drivers and turned the series upside down.
They got to experience the thrill of victory, visit the winners circle and make their mark in the Busch series. That's something that many of the more established teams haven't and will not ever get to experience. It is a very smart move to get out now, while on top, than to spend millions chasing something they have already experienced. It's likely that kind of decision making savvy netted them the win in the first place.
Congrats to them for such an amazing win
