Why are autorotations to a full touchdown not practised any more?
Too many broken off tail booms.  The Army can afford to replace damaged machines; flight schools that can barely afford hull insurance on recip helicopters in the first place, if at all, not so much.  (Funny story: I once asked an aviation insurance broker why the hull premiums on recips were so high, like over 5% of hull value back in the 80s (before Robinson's program).  He said, "Cuz they all crash!!!!" and laughed.  He said mainly it was because they are used for the most high risk activities: ab-initio training and Ag.)

Anyway, the FAA decided some years ago to remove the full auto from all but the instructor rating because, in a nut shell, it was calculated that the number of chopped off tail booms from training accidents attributable to full autos is way more than the number of chopped off tail booms from real full autos, where the hard landing could be blamed on removing the training requirement. Effectively, choosing one risk profile over another because the statistics favored it.  

Not too different from ending the old practice of live engine cuts during multi engine training.  Except for a simulator, a multi pilot never experiences a real engine cut on takeoff until it really happens.  Back when live cuts were done, there were way more failure-to-maintain-control crashes in training than crashes from real engine failures.