Actually, android fragmentation on phone is a horrible issue.
Even flagship phones people pay premium for ($1000+ samsung flagships) are only supported for 2 major os update.
The major reasons are two-fold:
1) android relies on binary blob supplied by silicon vendor (for example, qualcomm for snapdragon soc), which can introduce compatibility issues with linux kernel update since the drivers are not mainstreamed, and linux kernal space api are not usually stable (compared to userspace api compatibility which linus takes very seriously)
2) Reluctance of soc supplier to provide software update for socs older than 1 or 2 generations. In this case even Samsung is not providing firmware/software update for its own exynos chip for more than 2 years ish.
In automotive the same issue is worse simply due to the number of subsystems and suppliers (read volkswagen id3 issues). I don't think android automotive os has communication link to every single subsystem in the vehicle, let alone ota update).
Tesla infotainment system vs android automative draws heavy parallel to apple ios vs android. apple iphone 6s released back in 2015 is scheduled to have ios 14 update releasing later this year. While 2018 android flagship like samsung note 9 won't be getting major version update anymore.
Vertical integration really shines when you want to make rapid progress with an issue requiring networked communication.
I remember one of my old bosses telling me once, "Generic Solutions don't work", he was from an era when designing hardware and soldering wires was part of a typical software project.
Generic Solutions only work when mature layered standards are developed, the Automotive Software Industry seems to be a bunch of stand-alone systems that are hard to integrate....
So getting a car OS system to work well on one car is challenging, making it work on multiple cars with parts from different vendors is more challenging, supporting backwards comparability to ill considered legacy solutions even more challenging..
I don't think infotainment or even maps and navigation is the hard bit, the hard part is secure software control of the cars subsystems and software updates...
EDIT: This video seems relevant to the debate:-
Around 14;00 Sandy shows a single Model 3 high voltage cable compared to a bunch of GM Bolt high voltage cables.
The ;legacy car industry is only going to make EVs work by putting car bodies on top of standardized skateboards, while that saves money and does standardize a lot of the design, it means short term compromises.... particularly if a car company is mostly just using imported skateboards...
So what it all boils down to is no easy solutions and they can't leave everything to a last minute rush.
Again the video elegantly describes the dilemma, everything a company outsources, they no longer design or fully understand..