If you need a reason, the modem and the baseband firmware have several unpatched vulnerabilities on that model, which is not something that an Android update can resolve.
In a practical sense, what are the consequences of that? If you're careful about not installing random shit on your phone?
Well, it might be worth it reversing firmwares now with UART pins connected. A lot has changed in (agentic) reverse engineering.
BRB gonna try this out on my old Fairphone
Is there an easy way to tell if there are unpatched vulnerabilities in my phone's modem and baseband?