I'm not sure how 'most people' is relevant to the discussion. Fact is that it is one of the largest GDP exports for Vietnam and 5th in the world [0]. Just because you don't drink it, doesn't mean millions of other people aren't drinking it.
"The main destination of Coffee exports from Vietnam are: Germany ($384M), United States ($257M), Italy ($230M), Japan ($186M), and Spain ($150M)."
If I take those beans "shiny with oil" (aka: butter), grind them up and make a cup of coffee with them (I personally go with an aeropress w/ steel mesh), then there is going to be oil (butter) in that coffee. In fact, I can see a slight oil (butter) sheen on the surface of the cup of coffee if I let it sit.
[0] https://oec.world/en/profile/bilateral-product/coffee/report...