Mari and Luke were cute together; there were just better options.
I remember Luke dating Barbara Gordon, and I imagine Mari being older than their age group. They're adults who cares; superhero couples typically seem to be close in age tho. Even a gap like GA-Canary didn't have Dinah as an age-mate of Roy Harper. Feels like Mari dating Cyborg or Nightwing, which is how my head rationalizes Mari-Luke as a couple.