Why? Do the catsuits lose their healing powers when worn under a uniform? She could have worn a uniform right from the start, there was no in story reason why she didn't.
I vaguely remember it was some kind of sensor thing that linked to sickbay. Presumably it also helped sort out her necrotic Borg organic parts, and it’s clearly just covering some of her remaining Borg tech...the costume hints at this with the under corset. For all we know, it’s literally holding her limbs in place early on, and in some ways it’s upposed to be just a utilitarian covering. She wouldn’t give a monkeys about appearance, and certainly wouldn’t want to wear the uniform of her ‘captors’ as she sees them. The Doctor is either part pervert (likely) or again doesn’t see the point in anything more than a utilitarian skin covering (also likely...he does an aesthetic job on her face and hair, but he’s a doctor, not a tailor...his aesthetics are about the form of a body. He’s never even given himself holographic hair, as Picardo himself noted.)
In character terms, not wearing a uniform makes more sense. Whether it needs to be space babe is a production question.
I don’t think the uniform even takes out the space babe question, there’s plenty of discussion around all the nonstandard uniformed female characters in Trek, that always turn into a ‘she looks sexier with the uniform’ discussion at some point. I think some of us may just find uniforms sexy...
Outside of the narrative, you are replacing Kes, who did not wear a uniform. The thing about a uniform is, they don’t differentiate. Here’s this new character, she’s going to refresh the show...why put her in duty regs? Visually you are losing Kes, so you need a different texture in there. Not to mention designers love to have something to do...why just pull Daxs old uniforms out of the store and stitch Jeri’s name in after some tailoring?
Again...does it have to be shiney silver space babe?
But then we look at other things in VOY, Captain Proton, the Delta Flyer....VOY wears its pulp on its sleeve a lot of the time (even Banjoman, the 37s, etc hearten back to this Golden Age of SF era, and someof the stories and villains more so...Hirogen, Malon and Vidiians are all very pulp SF concepts.) so in some ways..yes. It was always going to be Space Babe. (It doesn’t hurt pulling in the teen audience either.)
The fact they overtly reference this and play with it so much in the narrative helps balance it out. (Of course Seven is the singer in ww2 holoparis, it’s just another classic Hollywood archetype...of course she’s the blonde with a heart of gold, and the scientist, and the metaphorical daughter of the lead, all for exactly the same reason...but she’s also smarter, stronger, faster and fundamentally less narcissistic than most other characters, but she’s arrogant because of her Borg nature, and naive in many ways.)
I gave up Voyager originally about the time she joined, but since returning to the fold, I think it deserves more credit. Sevens appearance is part of Voyagers Golden Age Subtext.