Aside from being a very hard to press "button", making you vulnerable to just about any pressure all the time until the very late game, Battlecruisers are vulnerable to many things.
The can be picked apart by well microed Vikings, they can be cost-effectively traded for with Widow Mines, they do not do that well agains Corruptors, Fungal Growth wears them down, they are vulnerable to Feedback, Tempests do great damage to them (though can not outmicro BCs), and there's also Blink micro to pick off stray Battlecruisers.
You are making an example of situation, which can not be used to judge Battlecruisers themselves - you were terribly ahead, your teammates having bought you time to amass an maxed out army. Yes, BCs are good for such army, as they are powerful per supply, so you can fit many of them into 200 limit, and have powerful upgrades. But Battlecruisers are not "a win". A maxed-out army of expensive units against a war-torn enemy is a win, that is.
As Day says, "Do not think 'X will be good in this situation'. See if you are able to get X, while still in the situation it will be good for."