It’s basically a “dark pattern,” especially when the UI gives different presets and highlights one as “recommended” even though that amount isn’t actually normal to locals. If nothing else it’s taking advantage of visitors who don’t actually know the correct local customs, or trying to subversively change the norm by guilt-tripping the customer into thinking the workers depend on tips the way restaurant waitstaff do. I think that’s the root of the feedback reflected in the original survey.