I remember an argument made in the context of a Stackoverflow blog post (one of the "which programming language do people use/like the most/least") that Ruby/Rails was dropping off in popularity because it was becoming more common for a new developer to have to work on the "legacy" Rails application (and therefore dislike it because they have difficulty understanding it the same as any application one didn't design themselves).

That seems to track with this if a Rails application is actually more likely to become "legacy" but it could also be the same for Python/Django. I just remember the Ruby/Rails point in particular because that's primarily what I work on.