The basic idea of an abaya is to hide your body from an outsider gaze. Hence an abaya is not required indoors. Secondly, the use of abaya is basically to hide your body from revealing its curves to a person who is not your blood relation. Therefore, it becomes acceptable to wear tight jeans or tops under a proper abaya coz no one knows whats worn inside (and no once cares to look at you). Also most abaya wearing women buy these erotic dresses displayed in showrooms for their husbands at home. I too was jaw dropped when i noticed the kinky dresses aplenty in the malls and almost everywhere. But the idea is to wear it indoors to seduce one's husbands and not instead to show off one's "assets" openly.

Freedom is the right of all sentient beings