How long does it take for Blizzard's Titan to show up? 4-5 years? How long does it take Diablo III to show up after hearing about it, 3-5 years? Since people can't wait 6 months for a major patch, it seems like an eternaty (spelling) for a game from a big company to show up. In my mind it is mostly about marketing.

If you release with no annoucement, you get less people.
If it takes you 5 years to make it, then if you mention it 3 years out, you can tell how many people want it by the people responding to the hype.
If you don't release when it is coming out exactly, you don't get other companies releasing products on top of your release and diminishing demand.
If you don't show all that it can do (no demo, no long gameplay trailer, etc), you don't get other companies copying what you can do and beating you to it.
If you don't like the game before it is released, why worry about it? Do you go around and say, "I don't like Olive Garden, why don't they just shut down?"