If there is no mechanism to “hold” blocks of seats for Holidays, they could forego the value of whole holiday itineraries in exchange for a bucket and spade seat. You do the maths.
Contributors on this forum regularly note how much more expensive seat only is on Jet2 than on other carriers. It is the same at other bases. That is to deter flight only and leave the aircraft open for IT packages they know they can sell. When the package sales start to slow down, they start to reduce the seat only fares. They are certainly not the only airline which does this.
Whatever the algorithm they use, not to do so would be commercial madness.