How do we know it's not Django/React?(not sarcasm; trying to learn) Adding those two to your link shows them on similar "these increase as rails decreases" correlations, with more area under curve:
Well, for one, stackoverflow trends are not the only criteria I'm using here. Recent GitHub projects, HN who's hiring threads, frequency of features shipped, and more are being factored in, personally.
Next.js is using React, it's a piece of the fullstack framework, like Rails and erb. React is the primary fullstack JS templating system, that's even more featureful as it's a better client side JS interop story than html templates.
By the stackoverflow graph, it's clear that most complex projects have moved onto frontend frameworks like React, instead of templated html, which standard Django is using. Django used in conjunction with a frontend framework, is most often through Django Rest Framework, which fares much less popular on stackoverflow trends:
https://insights.stackoverflow.com/trends?tags=next.js%2Cnes...