Why in Comics are they more scrawny heroines than genuine super heroines like She hulk and Electra?

Given the majority of those who purchase comics are (heterosexual) males there is a tradition of presenting female characters as sexually desirable to the male gaze. Heroines tend to be strongly sexualized (attractive, large breasts, tight outfits, etc.) because that is what the majority of comic-book buyers find visually pleasurable.

If one day society accepts that a woman doesn't need to be beautiful to be interesting, then perhaps women will be represented in more diverse ways more often. Right now, though, muscles are considered "unfeminine" by most people, and thus unappealing to male readers.

I think these narrow trends and ideas can be carried on by straight female readers as well, who may be more inclined to want to identify with skinny and stereotypically "beautiful" heroines, and thus prefer to read about them than more muscular or culturally "weird" ones.