Let’s just examine the change in Metal Gear Solid between 2/3 and 4 (yeah, we know MGS3 starred Big Boss, but they’re DNA clones of each other anyway). By this time, Snake had already grown a mullet and scruff, but all that paled in comparison to the broom mustache that happened in MGS4. We don’t even care that he got really old really fast. DAT MUSTACHE.
Did Snake just not care anymore? Was the Art Director at Konami (we’re assuming it was Yoji Shinkawa) unaware that only Western pedophiles rock that kind of ’stache nowadays? That shouldn’t be an excuse. Living in Japan, Shinkawa has probably seen enough of those suspect “English Teachers” from the US and UK to know that anybody with that facial hair pattern is a panty-sniffer.