It’s because the POS (point of sale) software isn’t customized for the application correctly. Either through laziness, ignorance, indifference, or a level of greed that only insane troll logic could make sense of
It seem to be best practice, and predatory best practice.
Some people fear of being jugded if they don’t follow the mass. And the tip screen make them question themselves like “everybody else tip, what will they think if I don’t ?” “What if someone watch over my shoulder and feel disgusting if I don’t tip ?”