I was really lucky to receive offers of admissions from a few of the programs that I applied to. I let all of the schools who accepted me know once I had made my decision (well before the deadline). Since then, a few of them asked which school I decided to go to instead (which I responded to since that's a pretty standard/expected question). However, one of the schools (let's call it University A) asked if I would be okay with telling them which school I decided to go to and also if I would like to tell them anything that can help them improve School A's program. Normally I would be fine with just telling them that I found a better research fit somewhere else because that seems to be the polite response, but I'm also not sure that would be an honest answer in this case. I basically knew a few hours into the visit at University A that I would not be going to that school because even though they had some pretty cool research, their department (actually, the entire university) was not diverse at all. Everyone was really nice, but I didn't feel like I fit into the "culture" of the department. Is this something I should even bother mentioning? It's very likely that I will see some of these professors at conferences so I don't want to burn any bridges, but I also feel like the lack of diversity was a very important factor in my decision not to attend this school (although I did take other factors into consideration). Would I seem too critical if I mention the lack of diversity? Are they mainly just expecting to hear people say that they took an offer with a higher stipend?