Surprisingly, I feel Mongo has been kind of surging back into developers' minds. I thought Mongo was utterly dead, and I also don't know why would one use Mongo instead of JSONB. The last I heard (3-4 years ago?), there were some fundamental problems with Mongo.

That said, I've incidentally heard a lot about Mongo in the last half a year. Might be my bubble. Might be MongoDB actually maturing and getting really good. I hope it's the latter.