I always thought the idea of using concrete was where the land may be at risk of subsiding. ie the stretch between Reedy Crk and Palm Beach due to much of it being reclaimed swamp. A huge amount of the M1 is on filled landed and so is at risk over time of subsidence.
Whatever the reason, I agree on the visibility problem re line markers in the rain. Surely there's some solution they could employee.
I will say though, that IMHO the M1 between Beenleigh and Nerang is the best bit of road I've driven on.

