I understand that we spill wine for the plagues. People died, they went through hardship, and it was not their fault.
But.... immediately after spilling wine for the plagues, we say that R' Yehudah made an acronym for the plagues - Detzach, Adash, Be'Achav - and we traditionally spill for each of those, too.
Why do we spill wine for a set of acronyms?
(Note: I'm looking for an a priori reason, not an interpretation of what that spilling means.)
To reinforce the question, why do we spill for Dam vaEsh veSimros Ashan, which are not makkos of Egypt at all, but rather a prooftext that ובמופתים is a reference to דם.
I think the answer is that the practice began with spilling / dipping for the makkos. To cite a note in a haggadah from 1590:
"I have seen anshei maaseh accustomed to dipping the smallest finger, called the pinkie (zeret) in the goblet and sprinkling the wine outside the vessel on each plague mentioned. And it seems to me that this is because it hints to כל מחלה אשר שמתי במצרים לא אשים עליך..."
From there, it spread to other instances. And thus, we spill wine for a set of acronyms that correspond to the plagues. And we spill wine for a prooftext from sefer Yoel that really has nothing to do with the plagues. This practice spread organically.
Any kabbalistic reasoning is ex post facto rationalization.
