The short answer: sexual dimorphism. Had they not been covered people would be complaining that the females and males look too alike, or if Bioware had just slapped a pair of tits on the females people would complain about that.
Eve and the salarian females’ garments also look ceremonial to me. Since she’s a shaman and they’re politicians, it makes sense. Personally I think Eve is just fab.
On another note, Eve is not the first krogan female we see in the series. On Tuchanka in ME2 there is an “emissary to the female clans” in the upper levels of the Urdnot base. She has a lighter voice and wears the same thing as the males, unless I’m wrong and it’s some kind of krogan eunuch (but that wouldn’t make any sense).