As an outsider to both: I think a lot of it is new/shiny. ruby on rails has been popular enough for most people to have seen the mess bad coders can make. Django never got as popular (I think it is older, but it for long has been an also ran).
The other half is ruby/rails got a reputation of being a language where some write-only code was encouraged. Djanjo and python have long encouraged writing maintainable code. This is a culture thing - there is no reason you cannot write unmaintainable code in python or maintainable code in ruby, but the reality is people didn't. This is part culture, part rails encouraged getting something working fast even if it wasn't maintainable while Django has also said take a little time to get it right in the first place and it will pay off.
The other half is ruby/rails got a reputation of being a language where some write-only code was encouraged. Djanjo and python have long encouraged writing maintainable code. This is a culture thing - there is no reason you cannot write unmaintainable code in python or maintainable code in ruby, but the reality is people didn't. This is part culture, part rails encouraged getting something working fast even if it wasn't maintainable while Django has also said take a little time to get it right in the first place and it will pay off.