Everyone would intuitively want the longer portion, so what Epicurus is doing is showing a way of looking at the issue that satisfies us that we are not missing anything new and categorically different by not having the longer time....
...This is something that a pig cannot do, but also something that does not appear (to us) to bother the pig. We have the need for the analysis only because it bothers us if we don't.
This to me points to some deeper ideas that I would love to get into, however I am short on time today so will have to come back to this later. I would say that if anyone closely observes the nature and experience of pleasure over time, then it will make sense.