Apple, for example, is famous for caring about things that rationally they shouldn't care, like the insides of their computers.
And since history is written by victors and we apply post factum rationalization, no one says that Apple is wrong to care about details that are arguably irrelevant to the success.
The same will happen with Tesla.
If Tesla is successful then Musk will be a genius with uncompromising standard for quality.
If Tesla will fail then Musk will be an idiot whose hubris, micro-management and inability to prioritize doomed the company.
And reality is that neither you or me have enough information to judge this decision one way or another. You weren't there and the it was probably more complicated that what you assume based on zero data.
According to reports Tesla started doing seats in-house when a contractor that was supposedly an experienced seat maker failed to produce Model X seats which contributed to 18 month delay in delivering the car.