What's with Elvis's movie wardrobe?

After just having finished Spinout, I have to ask: what's with Elvis's movie wardrobe? In at least two scenes, it looks like he's wearing three shirts - a turtleneck, a crewneck, and a vest - all under a jacket. Perhaps the turtleneck is actually a Dickie, but it still looks silly. This wardrobe style seemed to be the norm from the mid-1960s Elvis movies on. Why the need to cover up so much? It looks particularly dumb when he's singing by a swimming pool and most of the other people are in bathing suits and he's in a button-down shirt and long pants. In Blue Hawaii we saw him shirtless and in tight short shorts. In Girls! Girls! Girls! he wore short-sleeved polo shirts. In Kid Galahad he was bare-chested and just wearing boxing shorts during all of the boxing matches. It is true that his weight yo-yoed a lot in the mid-'60s, but in Spinout he looked pretty darn good to me. Why not show off those muscular legs? I'm sure I'm not the only person who thinks that some of these fluff movies would have been much improved if we saw fewer bikinis and more swimming trunks.