DD used to go to a swim class which was 6-6.45, and there was a class ahead of hers changing too.
Often, the smaller DCs in the earlier class (finished at 6pm) would get into pjs rather than back into clothes. They were cosy, easier to get on when damp, and saved changing again in an hour or so. Often, parents were dealing with organizing 2 wet DCs at the same time.
After DDs class, at 6.45, quite a lot got into PJs - having arrived in school uniforms. They were going straight into cars to go home. DD tried it a few times as she loves her fleece pjs in winter, but preferred to get back into her tracksuit (no school uniform so wears tracksuits always).
I can understand getting into pjs at that hour of night - if you are now nice and clean from the shower, and it's close enough to bedtime anyway so would be changing again in less than 2 hours. If the child is comfortable that way, and you are going home by car. Most had slippers and dressing gowns as well, under their coats.
But, as I said, DD wasn't a huge fan herself and, between a combination of using taxis with the au pair, or me bringing her and collecting her in the car, she was just happier in her tracksuits. But she was the kid who tended to get herself organized, and changed into togs, and back again, without any need for adult help (a classmate was in the earlier class and the DM used to comment to me about it - that the AP would be outside (DD and the AP had come to that agreement) and DD would rock in, find a tiny space, get herself into her gear and head for the pool with no bother - while there were DCs quite a bit older needing a LOT of parental assistance.