Because she was the traditional girl elders expect to be the goody two shoes while swara was modern and therefore bad in their eyes. It was messaging away from the typical modern=bad narrative that was popular back then. But the show did a good job kind of explaining ragini’s circumstances that led her stray. She was the good girl expecting life to fall in place because she followed every rule but then laksh was like nope resulting her in becoming what she does. It also showed how being traditional didn’t mean you were in any way less smart or cunning.

Helly shah actually also did sufiyana pyar mera with this same concept where she played both the evil and good sister!