Infix notation is preferred because the binary operator is visually close to both of its operands. The same equations as GP, but == is also postfix:

   > Commutative: a b + b a + ==
   > Associative: a b c + + a b + c + ==
   > ...

As expressions getting larger and larger the operands are getting farther away from their operators. RPN is great for computers to read and maybe humans to write (RPN calculators). Not so much for humans to read.