Not sure there is solid evidence for this. If you look at sources like the official census, the gender splits weren't that dramatic at all:
http://eu.finalfantasyxiv.com/lodest...e8ff1bcf34c5ae
If it's become worse since then, well, they've also been treating male characters like inferior customers since then. So it's likely a situation they caused themselves. Players who want the most content are going to be tempted to fantasia or quit when they keep being silently shut down like this. Correlation does not imply causation in every situation.