Green’s Dictionary of Slang

(US) used as an affectionate acknowledgement or emphasis, esp. when the previous comments have been negative; abbr. ‘But hey, what does it really matter...’.

1993		Strauss & Howe 13th-Gen: Abort, Retry, Ignore, Fail? [subhead] Xers Take it on the Chin – but Hey, That’s Life.
2002		Loch Dhu Dancers 🌐 Vegan Haggis —Anathema to the traditionalists but hey – why not?