Geographically. We already know the cultures are very different as a result of the divergence.
Let's be honest - even if they outright said they didn't want to make male Viera because they find the notion distasteful (or whatever), people would still be up in arms over the sexism. Hell, it might be even worse of a shitstorm if they said that. No matter what reason they give there will still be people out for blood over the very fact male Viera aren't playable - if they have a lore reason it makes in-universe sense, at least.
... saw this coming a mile away when Return to Ivalice was announced...
That's what I'm pinning it on as well. Despite what some of the media it puts out might have you believe, Japanese society is still pretty conservative. While I was a bit surprised at the lack of male Viera because I knew this would happen if it came to that, I'm... not... at the same time.
I'm not going to deny that it's sexist and hypocritical, but... have they said lore is why the male Viera aren't playable? Have they given any lore on the Hrothgar, let alone explanation as to why the females (apparently) aren't playable? Have they said male Viera won't be playable? Etc etc etc. It's not over until the fat lady sings...