In TOR, we see the majority of NPCs using uniformal blue, but that could simply be preference since we also see a lot of Mandalorians in armour of their own choosing. Perhaps the blue is a remnant of the Mandalorian Wars? Reminds them of a grander age? Or perhaps it's just in fashion. Shae Vizsla, Torian Cadera, Solus Bralor, Jogo the Carver, Mavrix Varad (and Clan Varad in general), Hondar Soongh, Tarro Blood and a whole lot more Mandos are using a more personalised look rather than the blue.
I think this has more to do with programming and less to do with story. Do you want every other Mando to have special armor, or do you want a new flashpoint?