Ah. That explains it, maybe.
I go to a gym that's also more of a club setup, i.e. various pools, saunas, tennis etc. I've seen more nudity there on 6 months than in all my previous gyms combined over the preceding decades.
It's not just a 'get changed quick and go home to shower' vibe, you do actually have a proper setup for moisturising, sitting down and drying your hair, doing makeup, etc, right? Besides, I find that spa people are way more body confident than the rest of the population. In mine, ladies of all ages, almost all white English, many older, are quite comfortable being nude or semi nude in front of others.
I'm probably one of those naked people, i.e. I'll be fully nude and not trying to hide it for at least 15-20 seconds while putting my swimsuit on. If I'm alone, it might be longer, but I appreciate in the UK people find nudity uncomfortable, so wouldn't impose my naked body on others.
Then again I´m Scandi and my childhood was spent chatting casually to all my class naked in the showers, sauna-ing etc. I don't think there's any close friends or family who I haven't seen naked and nudity of anyone doesn't make me feel uncomfortable. I just acknowledge the cultural difference and do not get naked more than necessary in the UK.