[asdf123wtf]

I think the timing was the most important factor.

Perl was everywhere (on Linux/Unix). Then Python came along an offered enough net benefit over Perl that it really started to displace it, and became the defacto scripting language that you would reach for when creating programs on Linux/Unix.

Ruby has some niceties over python, but doesn't provide enough of a net benefit over it for that same kind of displacement to happen.