Since the person responding to the queen ask doesn't know whether their side has all the keycards when the ask is below five of the trump suit, it is useful to play that jumping to 6 of the trump suit conveys the message "I have a trick source - bid seven if we have all the keycards", and to use 5NT as showing the queen, but denying any outside king. Over the 5NT bid, there is still room for a third round control ask or some other last train bid to still look for 7 if the asker is still interested.