IISc vs IITB

For what reasons, GATE (CS) topper (AIR 1) joined IIT-B over IISC in 2015 & 2016 while IISC has a better ranking as compared to IIT-B?

I have been a teaching associate to two courses during my stay in IISc and I have always asked the students a similar question. The common answers include:

1. Location - Mumbai Vs Bangalore - They like the pace of Mumbai and are not ready to adjust to the relaxed life in Bangalore. It could also be close to home.
2. Weather - They have never been to Bangalore and don’t know what a wonderful weather the Garden City has.
3. Research - IISc brings fear in the minds of a few less aware students, who have a preconceived notion about how strict IISc is and how there are no co-curricular activities. It is wrong.
4. Placement - The average salary of IISc CSE is perceived to be lesser than IITB CSE. Yes, there are no BIG TICKET placements in IISc where you hear packages of over 50 Lakhs p.a. But, the average salary of the entire batch will be higher than most universities and institutes in India.
5. College Life - The co-curricular activities range from music, dance, drama, poetry, sports - internal and external, study groups, study circles, technical groups like IEEE, SIAM, AHS, etc. There are way too many things to engage the busy or idle mind.
6. Peers - Your fellow students are Doctoral and Masters students with a very small fraction of them being Undergraduates.
7. Faculty - Some of the world class faculties teach in IISc. Interacting with them on Non-academic capacities brings out enormous positive changes in a person.