Adam Smith explains:
Republican leaders in Florida, determined to give the state a big say in picking the nominee, decided having their delegation slashed from 99 to 50 was worth it and set Florida's primary for Jan. 31. The RNC has said Florida will be a winner-take-all primary, but that decision is still subject to challenge.
My italics. Jim Geraghty adds:
If [tonight's] results are in line with recent polls, Mitt Romney will win 50 delegates and everyone else will win none. (Thus, Rick Santorum and Ron Paul spent a limited amount of time and resources in Florida.) But if it were proportional, Romney would win about 20-25, Gingrich would win about 14-16, Santorum would win about 5-7, and Paul would win 5-6. In other words, Newt Gingrich may have enormous incentive to file protests and perhaps even legal challenges to the RNC to make Florida allocate its delegates proportionally. It wouldn’t be Florida without a voting controversy, would it?