It's either the lack of care/prioritization (as they know customers will take most cars, at least they have up to this point) or the lack of capability. I do think that it's the former, as the latter exists in the global manufacturing knowledge base.
To your point, they are producing more vehicles than that plant should be capable of. Back in the day, we had a takt time of ~55s for the Corolla and ~100-110s (?) for the Tacoma. This means that we made ~980 Corollas per day + another 500 Tacomas. Call it 1,500 vehicles per day, or 360k per year, give or take. Tesla seems to be producing closer to 600k cars per year out of that plant, so it's clear that they're pumping them out at an incredible rate of speed.
Given that, if I were a betting man, I'd venture to guess that they sacrificed QC production line space and focus only on the safety-related checks. At this speed, they'd need quite a bit of space to do all of the checks for issues that we keep finding, and then having the space / personnel to fix them all. My guess is that they're just betting that customers will accept the cars as-is, and that the vast majority will not make a fuss about them; for those that do, they'll fix them later, and that's cheaper.
