Actually, from a technical perspective, Teslas are already pretty much completely autonomous.
Yeah, not really. I actually own one, y'know. And I've studied this stuff extensively.
Basically, there are a ridiculously large number of corner cases which "self-driving" fails to handle correctly. It's going to take decades to get them all implemented. Until then, you need a human to deal with the situations where the car goes "I don't know what to do", or worse, does something blatantly wrong.
It's pretty easy to implement self-driving on a well-maintained, standardized, Interstate-standards highway in good weather... and they haven't actually managed to do *that* reliably yet. The railroad tracks are an even more heavily controlled and regulated environment, so self-driving works perfectly there.
The problem comes with the idiosyncractic, irregular, non-standardized environment of city streets and rural roads -- which is most of the country's roadways. They're so far from functioning on these environments that Tesla specifically tells people NOT to use Autopilot in these areas.
Self-parking? Again, working in VERY limited environments. Well-marked parking lots or extremely well-marked garages or very well marked curbsides. The sort of places I park up here in Ithaca? Not a *chance* and nobody with a Tesla here (there are lots) has gotten it to work.