They lobbied and won against margarine back during WW2. It couldn't even be dyed yellow, you got a little packet of yellow dye to add to your white colored margarine at home. This lasted into the mid 1960s when they just started dying the margarine like butter.

Personally growing up on a dairy farm, I'm fine with making the distinction. Like you can't label food something that it's not. You can only call Scotch whisky Scotch only if it's made in Scotland. Same with cheeses and wines in Italy and France. It's a guarantee you are getting what you paid for, the real thing. And not some fake chemical concoction. It goes even so far as soap. Did you ever notice that Dove is called a beauty bar and not soap?

Go ahead and eat all the oat butter and drink all the oat milk you want if you like it. Oats are a pretty under used crop. The majority of it ends up as horse feed. Oats are a high food value food even for humans. I enjoy making oat bread. It's quick, simple, and tasty. Along side of a chili or soup, it makes for a hearty and nutritious meal.