I suppose it's possible that they couldn't even get that, as a potential reason. If the best offer was a 5th, they'd be better off taking the 3rd, even though it's a year later. Seems unlikely that they wouldn't have been able to get a legit offer for him, though. Usually the easiest explanation is the correct one, which in this case there are two options: that they either have no intention to resign him at all, or that they are working on a bigger deal with him.