IIRC, that is how spiritbonding works lore-wise. The more you are using the weapon it "attunes" to you, leaving part of your experiences in it. The Zodiac weapons being special due to just how much has been put in them already. (As an aside, I was half-expecting my Nirvana zeta to talk, seeing how it's heavily implied they get some form of sapience of awareness)

Edit: Aaaand disregard since Moose will probably explain much better in a few minutes