We all have our bad fashion times. We had the 1970s. Maybe the 2270s or 2380s were a similar era.
Maybe our heroes just lack any fashion sense and have no good judgment in their off-duty hours.
I'm no fashion expert, but what I find noticeable is the lack of general style in the future.
Today you might see a group of fellows in casual garb and it's similar... variations of jeans and tee-shirt, for example. Or another group wearing suits. Different colors and variations, but same general outfit.
It seems every time ST folks are in civvies, each one is in a wildly different style (one a leisure suit, another with flowing robes, another with pajamas, and so on).
In other words, we don't see O'Brien and Geordi both wearing the same kind of civvies the way two friends today would be seen both wearing tee-shirts and jeans together.
Whatever we see one fellow wearing, it can never be similar to what the next guy has on, the way people dress similarly to each other today.
Or something like this.