For fast prototyping, it's pretty hard to beat a NodeJS stack. A lot of modern web dev are one-man-shows. When you're just one developer doing frontend and backend, you don't really have time to care about database migrations or designing schemas. You really just want to duct tape enough pieces together to get your app out the door.

Caring about schema design, database migration, or even code correctness doesn't really help with this. Mongo in comparison has no learning curve, crazy number of pre-integrated libraries, and works well enough at low scale. This might sound like cancer to corporate devs but the tradeoff does make sense for individuals/demos/startups.

A illustrative case study: https://medium.com/unboxd/how-i-built-an-app-with-500-000-us...