Cheating at Poker is endemic for a few very simple reasons. First off, it offers the cheats at poker the best opportunity for cheating with the least risk. Since cheating at poker is mostly done through collusion techniques where two or more players secretly trade information at the poker tables and use that information to control pots by forcing opponents to put more money into pots when one of the poker cheats has the best hand. This is done by raising and re-raising pots to draw more money into the pot for the eventual winner.
The second part of the cheating at poker endemic, and by far the most enviable for those who cheat at poker, is cheating at poker online. Since there is virtually no governing body, those who cheat at poker can virtually cheat however they want without any risk at all. This has been well proved by perhaps the most notorious poker cheat ever, Russ Hamilton (the 1994 WSOP main event champion), who engineered the infamous Ultimate Bet online poker scandal through which online poker players around the world lost some $20 million. Hamilton, despite very incriminating evidence against him, has never been charged with any crime and most certainly never will. This is because with the mumble-jumble of insecure online poker governing and regulation, no one knows really who should prosecute what...and where. It's a lot more complicated than when an Italian man kills a Japanese man aboard a Norwegian cruise liner in South African territorial waters.
So for these two principal reasons, cheating at poker will continue to grow much more than cheating at any other gambling entity.