Students are the Borg. No, really, they are. No, they’re not a unified hive collective out to conquer. But, like the Borg, they adapt.
All attempts at teaching them are eventually adapted to. The techniques simply become ineffective. They no longer work in any way. Moreover, we don’t have a means to identify why these techniques fail.
Our sleeves and hats run out of tricks. We have nothing else to try, and, to be blunt, inventing new techniques is a losing proposition for us. There’s no money in it for us. We don’t get paid to research new techniques, to spend countless hours scouring the internet and getting in discussions to develop new lessons.
And the full-timers are immune. Their jobs are secured and they have no incentive to improve.
So the Borg, relentless, continue on.