The catch here is that players who use these cards often earn reward points for it as well as other perks.
If a player who has been loyal spends within $5000 - $10,000 in your casino but forgot to use this loyalty cards, if you were the casino manager will you still give them reward points for the expenses in the casino?
NO, because he didn't show his loyalty card and I'm not required to know personally all the gamblers, who have loyalty cards.
OP, why are you sharing with us this story? Did you forgot to show your loyalty card, or you know a gambler, who won big, but forgot to show his loyalty card? I don't gamble on local casinos and AFAIK, the local casinos in my country don't offer such loyalty cards. By the way, this is an interesting marketing gimmick and maybe more local casinos in my country should add it to their marketing strategy, in order to keep more gamblers loyal.