I have a friend who completed his MBA from the Delhi School of Economics. This answer is based on his opinions about why colleges with better ROI like DSE and JBIMS fail to compete with FMS. He has listed a few reasons for the lack of popularity of such B-schools:

1. Establishment: DSE MBA first began in 1986 whereas FMS was established in 1954. So the course and the institute are the oldest in the FMS case.
2. Alumni: Being an older Institute, FMS has a much stronger alumni network that has built a certain level of credibility in the corporate world. This criterion is missing in the case of DSE.
3. Courses offered: Until 2015, DSE offered courses like Master of Organization Development and Human Resources and Master of International Business instead of MBA. Firstly these specializations are not at par with Finance and Marketing. Secondly, MBA has more value than MHROD and MHIB.
4. Industrial relations: FMS is much more exposed to the industry and has excellent relations with the corporate world owing to a large number of its alumni.
5. Faculty: The faculty is almost similar as both DSE and FMS operate under DU. But the shortcomings are compensated for at FMS via the compulsory guest lectures by industry experts.
6. Crowd: The extremely high cutoff ensures only the most talented people enter FMS thereby increasing the quality of education and peer learning experience at FMS. This aspect too is pretty weak in the case of DSE.

It is because of these strong factors that B Schools like JBIMS fail to match the level of popularity enjoyed by FMS.