This is not just a recent development. Experienced folks can have issues unrelated to flying that prevent successful completion. It probably has more to do with attitude, willingness, difficulty with giving up old habits than it really does with flying ability.

I think the lower time pilots are probably easier to mold successfully.

I think there is also the very false impression that since it's a small plane it must be simpler with systems and easier to fly. This is most definitely not true.