While I understand this perspective, I'm hesitant to omit any elaboration, even if it's vacuous. It's a social lubricant.

If someone is invited to a party and responds with a plain "no," I think we would all find that very strange at best, and downright rude at worst. This does not implore the invitee to say yes -- rather, the invitee should at least provide a superficial pleasantry such as "I hope you all have fun, I'm unfortunately not going to be able to make it."

Substantively, that's a long winded no. But it goes over easier and I think many people appreciate that.