It requires a good knowledge and dedication to consistently return a new object (not mutate state). Further, chaining is problematic for tracing errors because so much happens on a single line. Ruby has many subtle features that can bite you in the ass.
Don't get me wrong, I LOVE RUBY, I would love these paradigms to be better suited (rbx/jruby come close). I just find if I embrace mutability, state, and OO principles in Ruby I am rewarded in quality by having other smart people who are more easily able to critique my code and better it.
The abstraction I (completely willing to admit being wrong/stupid) don't believe is worth it. I think less effort and more reward can be had using the right tool for that job. I, for what it is worth, came to my conclusion through the pain of trying.
I generally agree with the rest of your comment though, however I think some ruby code (per the original post) can be improved by introducing some of these paradigms.
And immutable structures with efficient "updates". Because otherwise every time you're altering the structure you have to copy it in full (though shallowly) then mutate it in place.