Because Dukat hated him.
Yes, but how does the Bajoran government know that that's not all an elaborate ruse to give Garak an excuse to stay behind on the station and spy on them? Even if Gul Dukat's hatred for him was genuine, he's just one officer. Garak could still be reporting to the Obsidian Order. WE know that that wasn't the case but the characters on the show circa Seasons 1-2 don't know that.
Later on in the episode, Ro pulled off a nice trick with her uniform.
Ro was part of the landing party that beamed down to a Bajoran camp. At the camp, Ro encountered a little Bajoran girl. Feeling sympathy for the girl, Ro took off her jacket and gave it to the girl. Note how she opened up her jacket from the frontside.
But just previous to her taking off her jacket, you can notice that her jacket (as well as the jackets of every other Enterprise Starfleet crew member) had the zipper, or opening, on the backside.That was a nice trick Ro pulled off.
Apparently, Starfleet uniforms may not be uniform from one scene to another. I guess it depends on the plot.
In any case, when Ro did take off her jacket, it was revealed that she wore a sleeveless shirt under that jacket. Actually, I thought that she looked good wearing that shirt. Too bad TNG didn't incorporate that jacketless-sleeveless-undershirt look more often for its female crew members. It was a good look. It was casual, yet it still looked respectable.
It might have happened, but I can't recall anyone else going jacketless (with that particular uniform jacket) during the series. Early on the series, there were crew members who wore the short sleeve and shorts getup. But that looked tacky. And on TMP, there was also a short sleeve version of the uniform that crew members had the option of wearing.
So it wouldn't have been unprecedented for there to have been a casual version of the Starfleet uniform that could have been worn by some TNG characters at various times.
Interesting. The only other officer I remember regularly doing the sleeveless undershirt look was Major Kira. Maybe Bajoran women have arms that get hot very easily?
As for her trick of unzipping the front even though the zipper usually seems to be visible in the back, I'm very used to costume's changing for the sake of the scene. Reminds me of the bit in Batman Returns where there's exactly one shot of Michael Keaton wearing the cowl without the black makeup around his eyes because he takes his cowl off in that shot and the character doesn't actually wear black makeup around his eyes. That's just something that they make the actor do because it looks goofy otherwise.