I think it was Joe Esposito who has said that Elvis was very uncomfortable with his growing weight and didn't want to be reminded to it by fitting new jumpsuits. Contrary to all other years he didn't want to try on new jumpsuits.
So with his changing weight the old jumpsuits were sent to the tailor who made them a bit bigger every once in a while. But after a while you can't make an existing suit bigger, so the amount of existing jumpsuits that fit Elvis were limited in 1977.
The tailor did receive an order for a new jumpsuit, but Elvis never came to fit it, so finishing it was a difficult task.