>>13
Because writing 1+2+3+4 is simpler than writing + 1 2 3 4
If you know anything beyond kindergarden math, you'll know that even in math where infix is used (only for historical reasons, the same reason why pi is used instead of tau), you still have a sum/product(∑/Π) symbol when you need to operate on variable number of arguments (sets) and functions are also called by their name first and arguments afterward.
Also, there is no such thing as ``natural'' in human invention, it's all ad-hoc, either guided by insights into aesthetics (such as with Lisp) or into idiocy, but more commonly by preserving tradictions, regardless if they make sense or not.