We'll need to ask @Craig Willis3 who authored the UPN spec!
What's great about the "given-when-then", it's cousin the user story "as a [role] I do [what box text] so that [why box text]", and skore notation (UPN) is they all help create shared understanding.
- human readable
- "bite size" sentences
- forcing to think about the context
There is probably other "notations" that i haven't heard about.