Hense, being exactly like hence, but instead of "This is why", it is "This is".
Hence "Hense why ..." is grammatically correct but "Hence why" isn't.
Person A: Hense why it's so similar
Person B: ERM AKSHUALLY THIS IS GRAMATICALLY INCORRECT
Person A: erm
wrong!
hence is this is why
hense isnt hence
Person B: What
There is no "hense"
Person A: says who?
Person C: Google