This is heresay and supposition but… I suspect the Columbian government is trying to figure out how to secure the value represented by the find, and the archaeological angle is one way to do that.
I don’t know anything about Columbia but I assume there’s some corrupt government officials there somewhere. Billions might not be a lot when talking about a country’s budget, but this isn’t part of their budget. Any gold that makes its way into someone’s pocket is fair game.
Again supposition but… I wonder whether Spain would have any claim on it if it wasn’t considered archaeologically significant.