They’ve become too easy.
It’s too easy to just dump any kind of data in there.
It’s too easy to query the database rather than cache data for a period of time in the app.
It’s too easy to join all the tables together rather than pick just the tables you need.
It’s too easy to write spectacularly, horrifically bad queries.
It’s too easy to copy/paste bad designs from the web that have gradually gained good SEO over time.
It’s too easy to install them and go live on really crappy hardware.
It’s too easy to scale for the first couple years because they just work.
Over and over, I see developers succeeding with specialized data storage platforms not because these new platforms are easy – but because they’re harder. Developers are wary of these new tools, so they’re careful. Developers pay close attention, read all the blog posts about it, the HackerNews links on it, and even dig into the source code.
If only they’d put that much time into learning relational databases.