Because the Audi doesn't charge users $10,000-20,000USD for "Full Self Driving," that's why we talk about it so much! If you throw it in as a safety feature in your deluxe package, and describe it as such, we aren't having this conversation. On the other hand, I strongly suspect that if they didn't do that, TSLA never gets to worth more than all other car companies in the entire world combined in market cap terms, and Elon Musk is never able to afford to buy TWTR, so one can see why he would do it.
What is the reason I should pay all of this extra money and still have to maintain full focus and attention on the road around me at all times? What is the market for it unless it's for me to be able to zone out more while driving?
Umpty-years ago I worked on robot tanks for the US Army, and we had a devil of a time answering this question. If the driver still has to be fully monitoring a single vehicle at all times, why isn't s/he driving it directly? What benefit does this not-quite real self-driving provide? Our soldiers told us that it mostly got in their way, because they wanted it go over here and the computer wanted it to go over there, and so they felt like they were fighting the computer more than anything else. It is possible that someone will come up with a better adjudication than we did, but it really made me question whether any level between 2 and 5 is actually useful to anyone.