Functional programming eliminates mutable objects, and mutable objects are (at a certain scale and in certain scopes) the new spaghetti code. I have worked with too many projects where twiddling the attributes of distant (global/static/inherited/etc.) things was necessary to get anything done, and it's obnoxious. It's too many indirections.

With functional languages and "dumb" data you don't have to guess about what your data can do. You just do what you want with it.