My Dec 2016 Model S has a "working" automatic rain sensor, it's just not as good as others I've seen. My '04 Audi A8 had a sensor so good that the first time it turned on I didn't know why, but then as I drove under some street lights I realized it had detected some really fine mist.
On the other hand, part of the reason I switched from the Audi to the Tesla was that I had $10k in broken "toys" on the Audi (1 of 2 bluetooth radios, 2 doorhandle auto unlockers, leak in the air suspension, steering wheel adjustment motor, etc), and part of what I wanted in the Tesla was something less expensive maintenance wise. So making more do less (using the cameras for auto wipers) makes sense.
I'd suspect the number of traditional rain sensor failures can probably be counted on one hand.
Tesla replace robust almost zero failure rate parts for cost only.
Only if you define "failure" as stops working. If you define it as not working, then it gives you a 100% failure rate.
The best rain sensor I had was in my old Ford Mondeo '04.
It's all about cost cutting to make EVs cheaper to buy
* no indicator stalks
* no forward/reverse control
* apparently the automatic rain sensor doesn't work/exist (I think that's always been true; I just learned about it)
It very much reminds me of Apple's backwards steps with magsafe, touchbar and the keyboard. Maybe they'll come to their senses but I dunno...