These companies fail because vertical integration, and even a monorepo, is needed to make these efforts successful. This is completely at odds with the existing OEM/Tier 1 business model and engineering process grown up around it. Also, neither OEM nor Tier 1 have software cultures up to the challenge.
This is why the Chinese OEMs, Tesla, and Rivian are able to move fast.
This is why the Chinese OEMs, Tesla, and Rivian are able to move fast.