Why hasnt a turntable manufacturer produced a table with automatic tonearm return/shutoff?

By extension, why are the spindle stackers no longer made? You could buy two copies of the record, put one on with A side up, second with B side up, and you can play both sides without getting up. And with each additional record, the tone arm is lifted to maintain correct VTA.

More seriously, there is a reason why automatic TTs are only found near entry level. The vast majority who are into vinyl embrace the inconvenience as a factor of appeal and value SQ higher than convenience. If it is that much of an issue, I suggest to stick to digital library of some sort, maybe CDs.

Additionally, once you get into more obscure vinyl, auto-TTs are more of a hindrance than a help. Say 33 rpm 7" or records with actual sound in runout. I have both.

I am using a Thorens automatic also.  It plays just as well as my previous 'audiophile' TT and is not nearly as fussy to set up.  

The spindle stackers were terrible because the records would get scratched when one dropped on another. as others have said, I think there are some decent semi automatic tables, but all that I know of that claim to be high-end are manual. I don’t mind getting up to turn over the record, but old men, at least this one, tend to fall asleep, listening to music and that’s a problem

the little fwend worked about half the time for me, but that likely had more to do with my ineptitude than the product

Personally, I prefer to have as few things in my turntable that can vibrate and adversely affect the sound - I also remove the dust cover when playing records -  plus, if it was a big deal for me to have automatic turnoff and return, I'd listen to CD's or stream instead. 

But I remember the old spindle stacker days when I was a teenager. I also often didn't bother putting records back in their covers back then! 

A lot of audiophiles assume something like you describe would add noise to the system (while have no evidence) but are happy to have monoblocks and all the connections that go with them. Go figure.