My answer is definitely bias (I really like MongoDB) however,
- I am guessing that institutes are using SQL because the people running those institutes grew up with only SQL and that is all they know and trust.To my knowledge, I think MongoDB can do everything a SQL db can. Change comes very hard for the Human specie.
- I do not think that SQL offers more security, especially if you use Atlas which is managed by MongoDB and runs on encrypted volumes for the 3 major cloud providers.
Check this link, which show companies using MongoDB
And i got it from this post