This article really does nothing to explain where this weird leotard based uniform comes from. Yes, the printing constraints contributed to it, but it originates with the circus strong man outfit.

The Atom's costume is a copy-paste job of this trope and being kinda strong is his sole power:

Early fans would recognize this design vocabulary, today we're just wondering what's up with all the spandex

There's also the unmentioned issue that flowing cloth is just straight up harder to draw than figure studies. Superheroes are essentially nudes without genitals and that's a whole lot easier to draw than clothing.