"God Knows !"
Force of habit springs to mind. Man has been cursing the Gods ever since he invented them.
Your observation that these are curse words is in fact the main reason, because they were literally that 'Curses,.' one man upon another.
"God Damn You !" I’m sure you can work out the variations for yourself.
In England a colloquial expression of shock or surprise, ‘Gawblime ‘ pronounced Gaw- Bligh- Mee, is in fact a corruption of “God Blind Me.”
Like so many other things in language if something is used over and over it becomes common and then the norn...