For marketing purpose or in other words to make a better service for players, it is obvious that covering the withdrawal fees will be better for the casino because there are many players who cares about withdrawal fee. I can say that even a few cent difference may make players choose the casinos with lower withdrawal fee (in case the casinos in comparison are all reputable). If casino can provide free withdrawal fees for players, of course it will be a big point for players but if casino cant provide free withdrawal fees, providing lower withdrawal fees will be much better.