The problem is that you need to architect, build, and maintain that system for years, or decades, to come. That requires an in-house software team that knows what it's doing. Building that first version that "works" is easy. Building that first version that actually works and supports everything you need it to, is quite a bit more difficult.

Building and then maintaining that software, year after year, without slowing to a crawl because of all the tech debt that's piled on (especially so since you have subpar engineers or you're contracting out to cheap workers abroad), is even harder.

And if you want to provide a user experience comparable to what the top software companies in the world are capable of, that's just not gonna happen at these car companies.

Tesla was born from the software industry, that's why they're the only ones that can compete.