The current version of MongoDB, imo, makes you super productive and scales without a ton of thinking. If you're working in Node.js, it's even more useful as the query language works just like a JS/JSON object so writing queries is super fast (compared to SQL where you have to spend a lot of mental cycles figuring out how to map object/array data).
I've found that denormalizing data (not even necessarily copying/duping data, but trying to centralize storage of it) when using MongoDB is the way to get the most value out of it. If you try to treat it like an RDB (which does work but can cause issues with complex queries), you'll run into headaches. If you just design stuff to be nested, though (and use the built-in APIs to query that nested data), it works incredibly well.
I think the key thing is that people using MySQL were having trouble with deep data and found MongoDB's document oriented approach much easier, but these days people are tending to start with PostgreSQL, which can handle that nicely.
(MySQL/MariaDB are far better than they used to be as well, though I find most stuff I read online doesn't take advantage of that as much as it might)
There's also probably a factor of Mongo solving pain points people had when they switched to it, and there being lots of excitement around that, where today the same people have run into the pain points of Mongo often enough that it's no longer nearly so exciting a prospect.
I wouldn't honestly be surprised if we're now at a point where people are -more- negative about Mongo than it really deserves, and I say that as somebody who viscerally hated it on sight and would still rather avoid dealing with it myself it if at all possible.
(oh and MongoDB the -company- has always done their best to be a good corporate community citizen, sponsoring all sorts of cool things as a result, and while I think the license change was a shame I -still- think they're doing their best, just in an environment where they wouldn't have a best to try to do in the first place if they didn't avoid being killed by AWS)
It is just my personal observation formed from working with Mongo and migrating systems away from it.
