It would be nice if the GrapheneOS dev would work it out with the FairPhone folks to make a device that could be supported. I don’t know why any company would hesitate to work with him, he is obviously doing good stuff, but I agree, Pixel only is kind of a turn off because it doesn’t seem like a long term path to building something sustainable in terms of both hardware and software. It’s a workaround.
Memory safety for one. C is very memory unsafe and that has been the source of a great, great number of software vulnerabilities over the years. Basically, in many C programs it has been possible to force them to execute arbitrary code, and if a program is running with root privileges, an attacker can gain full control over a system by injecting the right input.
I have very limited knowledge of rust, but from what I remember writing memory unsafe programs is nigh impossible as the code won’t really even compile. Someone else with more knowledge can probably give more detail.