Even still, mathematics isn't entirely infix. And outside computer algebra systems, you'll be hard pressed to find examples of the postfix operations expressed as postfix in programming environments. !, for example. What language allows you to express:

  n P k = n! / (n - k)!

as the above? `n P k` will become something like `nperms n k`, factorial will be moved to prefix as `fact n / fact (n - k)`. We're already diverging from the domain language, there's no reason to consider a more logically consistent framework in this case than one that seems to have arbitrarily moved some things from infix to prefix, postfix almost universally to prefix, and left some infix as infix.