I refuse to believe that the new IITs are less preferred by students considering their exponential growth and achievements. I don’t think that the new IITs are lacking in any way be it the campus or the placements. Most new IITs are now operating from their own modern campus with top-notch infrastructure. The average packages of the new IITs again prove that they are nowhere inferior.
The reason why some are preferred over others is simply because of location. Initially, Andhra Pradesh had the maximum number of selections in JEE so the IIT Hyderabad's opening and closing rank was better than other new IITs. Also, Hyderabad enjoys a better location than Indore. Personally, I believe if you are able to make it into the new IITs then getting old IITs isn’t difficult either. This proved that the new IITs are doing well and aren’t lacking in any aspect.