SQL never really left the table. People just like to try out new things and talk a lot about them. Its actually a pretty great feature of tech culture; we don't accept that everything is perfect, we always want to try for something better. And in this case, people tried to have a database with a different and potentially "easier" paradigm. Nothing wrong with that at all. But its hard to compete with years and years of tuning and optimization that SQL databases have gone through.