In many cases, ++ and -- are used to move to the "next" thing or the "previous" thing. Although this is equivalent to adding 1, the essential concept embodied in the operation is "next" or "previous", and not "1".(*)
The situation is somewhat analogous to the way many languages allow a programmer to write if (flags & BITMASK) ... rather than if ((flags & BITMASK) != 0). One might describe the former operation as "is the set of bits in common between the two values non-empty" and the latter as "is the set of bits of values equal to something other than the empty set".
IMHO, good languages should avoid requiring programmers to write "phony constants". If there's only one constant value that has a certain property, having a construct that embodies that property is cleaner than requiring that programmers specify the explicit construct.
(*) This becomes especially true if one views bytes of memory as being located between addresses, but with the convention that a single address will by default refer to the immediately following storage. Under this view, a 16-byte region of memory will have 17 addresses, with all but the last each uniquely pointing to the start of a byte, and all but the first each uniquely point to the end of a byte.
Viewing memory in this fashion, "incrementing" a pointer means that it should be made to identify an object that starts where the current object ends, and "decrementing" a pointer means it should be made to identify an object that ends where the current object starts. Note that in this scenario, there would be no space between the previously and newly identified objects.