Because the arrogance of modern Silicon Valley thinking is that "We are better, in every possible way, than older engineers, because we know code." And Elon Musk seems very, very prone to this sort of thinking (or, at least, his companies do, and I think it comes from him).
One example of many is the weird conversations he was having about sonic velocity robots and "lights out dreadnaught" sort of auto factories, which just about every other automaker has been trying on and off since the 80s, and has worked out that it doesn't work. So Tesla's modern lines, after quite a bit of fooling around with that sort of rubbish, look just like everyone else's lines, because as soon as you have humans in the loop for the things robots can't do well, you may as well run the line at human speeds.
One example of many is the weird conversations he was having about sonic velocity robots and "lights out dreadnaught" sort of auto factories, which just about every other automaker has been trying on and off since the 80s, and has worked out that it doesn't work. So Tesla's modern lines, after quite a bit of fooling around with that sort of rubbish, look just like everyone else's lines, because as soon as you have humans in the loop for the things robots can't do well, you may as well run the line at human speeds.