The exact reason for that is unclear, but Time's Karen Tumulty notes that, in the wake of yesterday's losing public option votes, things may be a bit too hot in Finance right now for triggers to survive. And that makes sense intuitively: Republicans not named Olympia Snowe almost certainly won't support the amendment, and public option enthusiasts like Sens. Jay Rockefeller and Chuck Schumer may not want to back a trigger at this point, for fear of foreclosing on a straightforward public option down the line.
Calls to aides to Schumer and Rockefeller were not returned before publication time.
Democrats hope to finish up work on the bill by the end of the week or shortly thereafter, and Snowe's vote at the committee level will be one to watch. A "no" isn't out of the question, and could enhance her leverage with respect to Democrats in negotiations over the final bill.