The rationale as to who is re-streamed and who isn't is often a total mystery to those involved.
When I went through training, the multi stream suddenly stopped. At least, for streaming direct from RAFC or BFTS, that is. The only way to be re-streamed was to have passed the Gnat course and the pre-TWU Hunter course at the very least. Why? Because 'They' didn't need many ME pilots.
At Brawdy one day, our jovial Flt Cdr joked "Well, if you reckon this is all a bit too hard, you can always volunteer for choppers". "Bollocks, Boss" we said, "No bŁoody way!".
All except 2 individuals who went and knocked on his door, asking to volunteer for choppers. "The only chopping you'll get is from me. Good bye, you'll be out of here PDQ" was the response - and off they went to become navigators.......
I was suspended from the Killing Fields of 237 OCU (along with many others...) in 1977 and went to Biggin Hill for Aircrew Reselection. Amongst guys there was one chap from the Harrier OCU and another from the Lightning OCU. I got Vulcans, the Harrier mate got F4s and the Lightning chap went to Hercules, later becoming very successful indeed. Interestingly, there were quite a few others down there and it was only those who'd taken it on the chin and got stuck in who were reselected back to flying. Even if that meant having to be deputy OC GD at Biggin as I was! Those who sat around sulking or playing Risk in the ante-room didn't last long - but it wasn't all gloom as there was a continuous supply of WRAFlettes who'd failed the old Fighter Controller course to add some interest to life.....
A lot of it is about attitude as foldingwings rightly says. But there's also a great deal of being in the wrong place at the wrong time as well.
But 'yoof' attitudes as exhibited on some of the Mil Forum threads (and I don't mean this one) clearly show that some people with the Wrong Stuff are getting through. Such as the little scrote trying to flog HM's property on ebay. Stealing from your mates, effectively - and something I was taught was one of the worst crimes in a society which depends upon trust to such a large extent.
Here endeth the lesson.
But good luck to all those who were unsuccessful at Shawbury. Hope that you get back in the saddle at some stage before too long.