Python is one the most popular programming languages. Ruby fits into a similar category as Python (high level, interpreted scripting language, very dynamic, has a rich ecosystem with tons of existing code). Being faster than Python makes it more attractive to use, or port Python codebases to.

Personally I don't care about speed for this category of language. I just bring it up because Python is one of the most used languages, is even slower, yet that's never held against it. Just seems like a lazy way to dismiss Ruby. Yeah, it's not as fast as C, Go, Rust or Java. Everyone knows and raw speed obviously isn't the point of a dynamic scripting language...