Essentially the wing sweep adds in loads of new and really nasty characteristics, particularly around stalling. These took a long time to fix, and even now the pilot's notes will say something like "if you get into a spin, eject immediately". Given that the aircraft of the time could only reach the Mach numbers required to benefit from this in a near-vertical dive and you can get 80% of the benefits from going to a very thin wing (as per the Spitfire, albeit for different reasons) then the average service pilot would not benefit from swept wings. It's worth noting that the the X-1 went through the sound barrier without much trouble, but the DH.108 was a deathtrap.Even more mystifying, when the Germans had figured it out in 1935, before the L.22 was even conceived. AIUI how this problem worked, it wouldn't even have needed wing sweep as such: that is, the spar could still attach perpendicular. It just needed leading edge sweep. Or have I missed something?
There's a little bit of it in the video below - it's worth noting that all the swept-wing spinning is done in a Hawker Hunter, which is almost unique for a swept wing aircraft in that it's actually cleared for intentional spinning. My understanding is that the ETPS is unique in teaching spinning a swept-wing aircraft, simply because they have a Hunter. Other aircraft can be spun if they have a recovery chute, but that isn't an option for a service aircraft.