Why don't phone GPS maps give scale?

The online maps do (I just checked), and ordinary maps do; a little scale icon would be immensely useful considering how easy it is to zoom in and out of a map on a phone and lose perspective; and it wouldn’t take up much space, just a tiny dashed line with some tiny words indicating feet or miles. So, why wouldn’t phone GPS maps give scale?

(Putting in social for the relaxed rules, though I would appreciate some serious answers too! This is a serious pet peeve of mine, aha)