Basically, Tesla does not pay enough here for competent people to work for them.
EDIT: For mechanical and civil engineers, they pay ~10-20% more than market average, but market average works 9-4 (35h/week), has a pretty relaxed work, colleagues are also relaxed, etc. These type of people are used to a very relaxed life, spending lots of time with their kids, leaving their work phone at work, not checking emails after work or on the weekends, etc.
In Tesla you work your ass off, work shifts, there is apparently a high level of incompetency, high turnover, lots of stress to deliver impossible things, etc.
A very skilled friend told me he wouldn't do it for less than 3x their actual salary. For 20% more the offer made absolutely no sense. I think he was there for ~2 months or so. He took a pay cut for their next job, and did so very happily.
If the only people you can attract are juniors without anybody to help them grow, well this is what you get.