In poker you have an easily identifiable edge (crap players), which never goes away. In trading you have no easily identifiable edge, and most identifiable edges disappear after a few years as the inefficiences get exploited or just go away. Therefore, making profits from trading is much more difficult than in poker. Secondly, poker has clearly defined rules and possible hands, and table stakes means your loss is limited; in trading, the markets do not have a limied number of "hands", but can have unprecedented moves, and due to leverage you can lose more than you have in your account - this results in trading having much more risk than poker. Third, trading has running costs such as charting, internet connection, office space, slippage, commissions, news sources etc, whereas in poker you get comps for live games and only pay when you win a pot. Fourth, psychological issues are much more critical - in poker when you go on tilt, you generally only lose what you have at the table; in the markets if you go on tilt, you can lose everything you have and go into massive debt. Finally, the minimum stakes in trading are higher than in poker, and there is no "easy" table to play at, equivalent to $3-6, where you can learn your skills. All this IMO makes trading much harder than poker. The advantage of trading is that if you crack it, you can make much more than in poker.
