Part of the issue is that phone manufacturers actively make this difficult. Hardly bootloaders are unlocked, barely any drivers are freely available, all the hardware is so tightly intertwined & locked in that you can still brick these things with no recourse (though this has improved). Not to mention 3rd party apps that have built with dependency on Google Play Services which needs to be replaced, banking apps with "security" attestation - using free software on a phone is magnitudes more hostile than doing so on a PC.