It seems like on some routes that Spirit is waiting to see how advance bookings are as opposed to just assuming that some times will be less popular than others. For example, I couldn't find a single 2500 mile reward on the CLE-DFW route last night, checking the low periods from September to February of 2017.

The same with CLE-LAS for January and February of 2017. Although November and December of this year have the cheap reward level flights on some dates, it is now within the 180 days mostly, forcing people to pay the award fee.

I love Spirit, but the airline seems to be acting a bit strange and "not as good" since Fornaro took over as CEO.