I would say the main issue is that somebody has to do the porting, and that nobody can perform magic .
Fairphone OS is Android 9 currently.
/e/ is Android 9 currently.
The emerging LineageOS 16 is Android 9.
Android 10 GSIs and even an Android 11 GSI are out there, but donโt work on the Fairphone 3 so far, see [HOW TO] Flash a custom ROM on FP3 with GSI.
I think the first important step would be Fairphone releasing an official Android 10.