

The more full reason is that the device is still encrypted prior to first unlock and is harder to extract any information from. As to what you said about police requiring you to enter your PIN, they can’t. You can’t be forced to reveal your passwords/PINs but they can legally force you to unlock biometrics (fingerprint/face ID)
The short answer is in many cases it’s just not worth it. Maintaining a Linux build is not free and the possible market share gain is fairly minimal. Add to that the possibility you get it for free through proton and your reasons for investing the dev effort shrink.
I’ve heard an argument for maintaining Linux builds because Linux users will provide better bug reports but that mindset is unlikely to ever survive in a big studio