primarily due to the airlines that once recruited from the hold pool running their own pre selected schemes
The airlines are running per selected schemes but the easyjet cadet scheme only come around every year or so and they only take around 15-20 cadets each time however, they need to recruit 200+ a year so they will need more than 15-20 pilots so they will most likely use the ctc hold pool.
Even if a ctc wings cadet doesn't get place through the hold pool he is in the position of a modular graduate and since this is a 'modular vs integrated' debate the hold pool is surely an advantage