[jkarneges]

I'd say the success of Parse and Firebase have a lot to do with the fact that they are services, especially public internet accessible services (in contrast to a host of DBaaS options that are meant for "behind the webserver" use). Maybe if someone created a version of MongoDB that could be safely accessed from the browser, it would have been just as interesting?

Or maybe it really is about the simpler APIs that Parse and Firebase provide.

Or, maybe Firebase is mega popular due to the realtime change events. Too many variables. :)

[bontoJR]

I would bet on development speed. Using SQL and No-SQL software brings a lot of engineering, you have to decide where to host, how to host, who is going to take care of that. This translates into costs. After that there's a new bunch of problems, it's required to engineers to know the platform and create the software for that. After that there's maintenance, etc... all things services like Parse and Firebase removed, with the trade-off of less flexibility, but as I said before, this can be a problem later in the development stage...