First off, this is in no way intended to bash Bethesda or their marketing strategies, it's merely a question I truly do not know the answer to.
In July 2013, the film Batman vs Superman was announced. Filming hadn't even started at that point. It was originally intended to be released in 2015 but has since been delayed to March 2016. So there is an almost three year gap between the announcement and the (as it now stands) release. The announcement was just a little teaser, with news slowly getting out over the months.
Now I'm wondering; Is anyone going to skip this movie because it was announced too early? To be honest, I think not. I don't believe anyone will say "I've been a massive DC fan my entire life but I will not watch this movie because they didn't keep us in the dark for longer than they have."
Grand Theft Auto 5 was announced in October 2011, it was finally released in September 2013. Yet people still bought the game. Quite a lot too. Apparently not many people decided that the wait was too long and decided to pass the game altogether.
So here is my question: Why does Bethesda seem so insecure or secretive about their game announcements? I'm not talking about a choir of angels in power armor with Todd Howard in the middle launching a nuke and having the smoke read "FALLOUT 4", just simply letting the fanbase know what they are working on. A bit of info would soothe a lot of fans' nerves, I think (lol). There must be a strategy behind this, Beth must believe that keeping the fans in the dark will somehow lead to more sales. Why?