Getting back to actual question: Elisp supports "real" lexical scoping since previous major Emacs version, and it has had "lexical-let" and other such forms since forever, but most of the code is still dynamically scoped. In practical terms it's similar to having every variable declared as global - it allows for "out of band" communication (outside of arguments passed/value returned) between routines. This is sometimes handy if you want to change some function behaviour in a way that it didn't think of (ie. it has no argument dedicated for this). As a very contrived example, if you have a routine which beeps furiously every time you invoke it and you find it unbearable (I did) you can instead call it like this:

    (letf
        (((symbol-function 'beep) (lambda ())))
      (beeping-function))

On the other hand, every out-of-band communication has a set of problems to it: you can forget to check it, or you can accidentally pass something to a called function you didn't want to. In practice this is worked around with using longer, prefixed identifiers and the semantics of `let`. As long as every variable your function uses is let-bound inside it it is essentially safe to call with any kind of environment, as it won't ever look at it. Most functions are like that.

In short, dynamic scoping has it's advantages and drawbacks, and it feels quite well suited to an extension/scripting language of an app. It makes certain patterns easy enough that they don't even need a name ("monkey patching"), and it makes others much harder (like the linked dash-functional library, which would be very hard to write without lexical-scoping: t).