May be because the people are blogging from across the country and it's not possible for everyone to go and see the occupancy rate of each train individually. All they can see is the availability of seats in the train and current availability. The attached screenshot shows the availability of seats from CDG to NDLS in all 3 Shatabdi's. Even though seats are available on all the 3 shatabdi's, 12045 stands out as a poor performer. And this is just General quota, tatkal quota are all vacant for tomorrow. People call such kind of trains as Flop or WE.