I would imagine it has something to do with the fact that they simply aren't fun. No one wants their hard work go down the drain simply because the RNG decided there would be an earthquake in your capital. Realism generally gives way to fun, or at least gives way to not arbitrary punishment.
Edit: My reply was on the assumption you meant random geographical events, which a rereading revealed was not the case. You are referring to historical geographic events. I would still say they wouldn't be included, but for the reason of foresight. A player playing as Spain would obviously wait to invade England until after the giant storm which would wreck his armada, and a player playing the English, knowing the storm was coming, would prepare a counter attack. Simply gamey.