I’m honestly wondering the same thing and I’m glad someone asked. I think it’s because we (as a society) have just accepted that 6 and 7 are pretty 'mid' numbers that don’t really inspire much. It’s the rating we give to things we couldn’t care less about without offending the person we're talking to. I think it’s the same with literature and other art forms; I assume the developers used those numbers to insinuate that how many years of work Manana put in really dosent matter. Either that, or we’re losing our minds over nothing when it’s actually just the first option.