There is also the factor that, with the army shrinking towards 72K, there is a smaller pool to select from; along with increasing demand for their use which lead David Cameron to funding a requirement to increase the size of the regiment in 2015. With the lag between decision being made and the funding and task reaching the frontline the timing seems right.
If you have a requirement for an increased output one method to achieve is to accept marginal candidates and accept the increased failure rate if it produces even only one or two more graduates at the end.
I think a lot of pilots know of the fluctuation over the years when capable students were chopped in one year and marginal ones recoursed and then passed the next.
David Cameron promises to 'beef up' the SAS to take the fight to Isil - Telegraph