Sei nicht unverschämt!

This seems almost like the word “shameless” in English in terms of its internal logic…I was surprised to see my usual dictionaries not list this as a translation. Leo.org lists a variety of words, such as “barefaced”, “brazen”, “impudent”, and “insolent” which seem close in meaning to “shameless”.

Is there a reason it is not usually translated as such?