> python succeeded because it wasn't Perl's TMTOWTDI, everyone expected ruby to overtake python, but .. for some reason that never happened

Ruby allows (and to some extent encourages) unreasonable code.

It's not bad code (and in some cases extremely elegant), but it's code you can't reason about.

Being able to open any class (or object) and add new methods to it makes tracking how execution works extremely difficult.

The language allows for very undisciplined things to work - its great for the "scripting" and rapid prototyping - but unless you're going to throw it away the next day of having to maintain that code it starts weighing on the future speed of working.

Undisciplined code can be handled by making sure everyone on the team is disciplined in its use and documenting how things work... but that rarely reflects reality.

And so, you move to a language that enforces more discipline in how one uses it and is more reasonable in its execution.