I'm relatively well informed but I always just assumed oat "milk" was an inferior substitute marketed to the actively or wannabe lactose intolerant. [EDIT: and vegans of course.] (No idea if "wannabe lactose intolerant" is really a thing, but i'm thinking of the way gluten sensitivity became a faddish self-diagnosis for a while.)

I still don't drink the stuff, but it's only dawned on me in the last year that there are other reasons, such as environmental concerns or ... actually, I'm not sure. Opening two tabs to Google "oat milk why" and "oat milk why site:reddit.com" now, which conveniently makes this relevant to TFA :)