Phones should be like PCs - they give you the hardware, and you figure out what to install on it. Unfortunately Linux imo is partially to blame here - if they decided to do a stable driver ABI (don't hate me, this was the norm outside Linux and open source OSes), you could easily separate the OS and drivers and update the m separately.

The missing link here is ACPI, unlike on PC, the hardware doesn't describe what it has to the OS, making the task much harder.

The lack of standardization of handled devices is also another factor, they might look similar or even identical but they often are different per region and have some hardware revisions.

Android does have a separate driver partition nowadays but that doesn't help too much.

Who is "they"? Linux isn't a person or an organization. The people (and organizations) contributing to Linux are all doing it for their own motivations to solve their own problems. You are asking them to make their lives harder, for free, in service of fixing an issue that they don't care about.