In principle, a 1-tuple shouldn't even be a thing - any single value is a 1-tuple by itself already. However, in a dynamically typed language, this approach complicates things elsewhere - e.g. if you have a value / 1-tuple that is a list, you'd expect iteration over it to give you list elements, not the single element that is a list. But if you have a value that is a tuple of unknown size, you don't want to special-case iteration for when that size is 1.
It depends what you mean by tuple. In Python, tuples are basically just immutable lists. Just as lists with 1 element are useful, so are tuples with 1 element. You might be dealing with a tuple of unknown length, where the length could be 1. In other contexts, the word "tuple" often carries the connotation of "having a known fixed length", in which case the notion of a 1-tuple as distinct from the value itself is less useful.
