Because in the same paragraph, it is also mentioned that this
is a prvalue
("pure rvalue").
Examples mentioned in the standard for pure rvalue are the result of calling a function which does not return a reference, or literals like 1
, true
or 3.5f
. The this
-pointer is not a variable, it's more like a literal that expands to the address of the object for which the function is called ([class.this]). And like e.g. literal true
has type bool
and not bool const
, this
is of type X*
and not X*const
.