"You have to be ashamed."
Translation:Вам должно быть стыдно.
December 16, 2015
Because it's the way Russian grammar works. Sorry, I don't know what answer you expect. We never omit быть as an infinitive.
«Вам должны́» means 'someone owes something to you'. «Вы должны́» means you should/ need/ must / owe something.