Jaipur and Agra Fort are the Very Important Tourist Places in Indian Tourism, lots of tourist movement is there between these two places, so first shatabdi priority should have been given to them, not Howrah NJP, as they are not that much reputated in respect to tourism
And secondly there are very very few trains from Jaipur to Agra, not even there are from Kota and SWM, but there are lots of trains between NJP and HWH