Yes, this would be my hypothesis too. I see Hollywood epics all the way from D.W. Griffith (and the studios that made them) wanting to broadcast an aura of grav

Yes, this would be my hypothesis too. I see Hollywood epics all the way from D.W. Griffith (and the studios that made them) wanting to broadcast an aura of gravitas. And nothing does that like using pretentious Roman numerals. Of course it's all convention nowadays.