You would typically put the this pointer into the first argument when doing OOP in C. You can put the this pointer in the last argument to have it work too. However, you cannot omit it entirely. That is something that is not OOP. It is an ADT.
So suppose you have it, but never use it. Then why have it you can just remove the first parameter. You can have object methods in C++ too, that don't use the this pointer.
Also why do you care exactly about the order of arguments? The nature of the function doesn't change, it's entirely arbitrary and orthogonal to the paradigm the function implements. Another example is the implementation of the equality operator between objects. In languages with syntactic sugar you typically have (self, other), but if its the true equality operator then the order doesn't matter.
