It's understandable. People tend to forget the obvious, that the primary goal of Mapbox is to make money. Investors have given their money to Mapbox with the expectation that they will get back more, preferably much more.
At least 50% of my work projects happen because the resources I'm using are free. If it isn't free, the project either doesn't happen, or I spend a few months coding what is missing.
So I'd rather they tell me upfront that I can't afford their product than waste my time.