Buster was the "last man standing" of IPC's comics empire. It was where all the lesser comics effectively went to die, so by the early nineties it was kind of a "greatest hits" package of the most popular characters from comics past. Sales were still strong in 1999, apparently it was cancelled simply because nobody could be bothered to keep it going any more.
You can see the very last page of the very last issue here, with all the characters coming to a suitable conclusion. http://www.bustercomic.co.uk/issue15.jpg