Ticket price? More likely they couldn't afford to park in a Disney lot. IIRC, unlike Disney Land, the ticket booths for entry are between the parking lots and the station for the monorails that take guests to the parks, not the park entry plaza (between two parks like at Disney Land). IOW, their "die-in" would have been in the parking lot(s). Whether concrete or asphalt, I suspect the temperature of the surface on which they would have lain down would have been quite unpleasant, also.
All in all, this cancellation reeks of avoiding a very public fizzle.
Anyone else notice the irony that a group supposedly inspired by the Pulse shooting was targeting a business the Pulse shooter scouted but rejected? Perhaps they're lashing out at WDW for not having been where the shooting happened? Sick A-holes gotta be sick A-holes.
Since they are targeting a particular political candidate, I think the IRS should look into the group's tax status.