Here is another aspect of this: The "leaking vessel" analogy is clearly an important part of Epicurean analogy, as illustrated at least once in the opening of Lucretius Book Vi.
So the discussion of "filling vessels" is an important aspect of discussing how Epicurus taught to lead a life of pleasure.
I would argue that the key question is what is it about these desires/vessels, other than that they start off empty or are empty at a moment in time, that prevents them from being filled?
The issue cannot be solely that they are "empty" at a moment in time.