I also don't understand this. Even today, Rails is, by far, the most productive environment that exists for developing a web application. I speak this as someone who also wrote a ton of backends in Node.js, Java, and many other languages (never tried Django though, so I don't know about that). Almost all of those applications would have been 10% of the effort if they were just Rails apps.
A sibling comment here mentioned that Rails' power came from other gems, but that's not really true. Rails is still actively developed, and just Rails, by itself, gives you more functionality out of the box than whole 1000+package Node stacks.