This sounds like something Elon musk would do to Tesla just to save $8 on parts
I don't think you understand what $8 per vehicle represents in cost savings.
$8 in parts can literally be 10s of million in savings per year.
And then you are basically tied to this supplier forever as switching something so fundamental isn't easy.
In automotive, using less screws to save 50c on each vehicle is considered a big win.
A clever one I saw was where they milled a PCB thinner in a section to make it bendy and did not need 2 boards because of this.
Not just for V1, but the following version as well. Once you have an internal team, you can vertically integrate and costume the solution to your needs exactly rather then buying a generic part from a supplier.
Things like OTA updates are just easier if you control the software and hardware stack yourself.
And once you have a team with expertise you can use them for other projects as well, like Dojo.
That's at least a few engineers salaries. ;)