There's nothing complicated about using it.

I'm not talking about using the pipe operator, I'm talking about implementing it. The C++ version is ridiculously complicated.

Let's compare your code with an analogous implementation in Common Lisp.

  (defun pipe (val &rest fns)
    (reduce (lambda (acc f)
              (funcall f acc))
            fns :initial-value val))

Just this allows for some pretty similar code:

  (pipe 99 #'1+ #'sqrt #'1-) which evaluates to 9.0

It is possible to implement it in C++, but the implementation winds up being ridiculously complicated. I just implemented something very similar in Common Lisp and it wound up being incredibly simple. Why doesn't C++ allow for a definition nearly as nice as the Common Lisp one?