Source required.
But I'd like to provide another anecdote just for fun, from 6 years of living in Spain beginning 20 years ago. It was, at that time, certainly considered unique to shower every day, in a mid-sized northern Spain city. Unless every other friend in my residencia was weird in this regard, which is unlikely.
Interestingly, they also had a communal pool. Swimming to them rendered a shower that day unnecessary. Note -- I didn't notice any notable signs of bad hygiene, though.
Anyway I'm sure there are studies that show we're all converging on similar routines!