I think a big part of the answer to 'why would you want to be a Sgt pilot...' is the result of the commissioning process as observed by said NCOs.
Every NCO knows x people who were damn good at the job, excellent at running their wet/dry team and so forth, who got knocked back while some complete weasel who couldn't be trusted to read the FRCs unsupervised seemed to absolutely waltz it. I realise that the process isn't actually trying to locate Dan Dare/Biggles - but the amount of times Frank Spencer makes it tends to disillusion at times.
So if you don't have much faith in the commissioning process but want to be a pilot, then NCO pilots looks to be a good move....to an NCO. That NCO would almost certainly prefer a commission, but the pilot slot is the main draw.
It might also help retention on the frontline - NCOs eager for frontline flying for as long as possible, without the distraction of wondering whether the career would be better served by becoming a tea boy at MOD.
For the more dismissive on here - try checking the educational qualifications of your NCOs, when it comes to learning how to fly was the Modern Studies graduate up front really a better bet than the Maths graduate in the back?