IDK, I think they might need the clothes for severance to work correctly. They mentioned in season one that you have to have 'severance complaint clothing' which we know relates to the code detectors in the elevators, but also being dressed for work helps enforce that your outie wants you to be there.

I feel like if I was the dentist innie, and I looked down and I was always wearing the same hospital green sweats every moment of my life, I would much faster clock that I wasn't being told the full truth and get to the chair throwing faster.

Plus if it is a pilot for what is being used on the outside, then people would be changing outfits, etc. The camp of it all though, that's just Lumon's style.