1. DraftKings and FanDual are US based companies, most of the big poker sites were not.
2. There is an exception for fantasy sports in the Unlawful Internet Gambling Enforcement Act. You can debate whether Daily Fantasy Sports should qualify, but unlike poker it is at least starting on legal ground.
3. Daily Fantasy Sports has buyins from the NFL, NFLPA, individual teams, ESPN, the major broadcast networks, etc. Lots of peoples' hands have been greased from all of the money DraftKings and FanDual have been spending on promotion.