I dont think they can just "port" and nothing is as easy as it seems. destruction mechanics and codes from a different game. Then you got maps with BF3 and BFBC2 codes.....
I also think they very much wanted to move away from 2042s negative reception as well. We also have the godot map creator so the community can make some of these maps themselves.
If i could choose maps for dice to bring into this game however would be reclaimed, flashpoint, exposure, haven and redacted. So pretty much all the seasons maps.
At that point you might as well play both games and do 2042 during BF6's downtime in between seasons. Its cheap enough.