ELI5 - explain like i'm 5 (years old)

I've been watching for over 10 years as people try to load various operating systems on different mobile devices. A common theme has become the table that lists which bits of the device are working, partially working, or not working.

I understand this is mostly because hardware components have closed-source drivers, right? Why is this such a large barrier? The lack of documentation on how to interface the binary blob? (assuming a similar kernel)