Because Applejack has to be a half naked whore, doesn't she? Clothes like that aren't sexy. You just made an amazing character seem like worthless shit. I'm only faving this because you have good style and for Fluttershy.
Actually, sometimes people who do hard work dress in casual clothing, because formal clothing like Fluttershy's would just get uncomfortable and chafe. Especially if you're like Applejack and you have to toil in the hot sun sometimes, so Applejack's outfit works for purely practical reasons.
After all, don't most of us dress in less clothing in the summer?