Could be habit I guess, if you're really used to something it feels extremely weird with something different.
Took me years getting used to not having something against my back, even those times I went topless in the past I carried a bag or backpack against my back, shower had waterflow..
So felt extremely weird suddenly having empty air behind my back, used to it now and thus can sleep without any sheets over me just fine. (About time, way too warm weather down south.) =p
Anyways, Yuki had a surprisingly neutral choice compared to the usual stereotypes, reminded me of a guy I know when he's wearing shorts and one of his too-tiny tanktops or w/e they're called.
The rest were rather expected but still decent choices:
Asuka that usually wear something under skirts to hide her underwear, now wearing something that covers alot without hiding much of that shape.
Mayu picked something fairly feminine bordering towards what she'd consider too eyecatching, despite providing the coverage and making her shape less obvious just as she wants.
As for Kei, a good choice if you're just after having some fun bathing and such without adding needless unwanted distractions.
(One of the few choices that aint likely to cause teenage girls gossip about glimpses and shape.)
If you want to change how someone see you, better focus on how you can do so without straying too far from what you're comfortable with or it might very well backfire.