Bad coffee beans if not roasted to charcoal state taste even worse. Argument that that most of available coffee in VN is made from pretty bad beans, so roasters have no other way to roast it to that level.
That's it.
Meanwhile, people that don't mind "burnt coffee" are the people that preferred coffee-based drinks from coffee shops. If I get a salted caramel mocha Frappuccino with two pumps of hazelnut - burnt beans are probably the only kind of beans I will be able to taste in that drink.