My pet hypothesis about why shower is often praised to be such a mindful place is that it has not so much to do with water and more to do with the fact that for many people life alternates between 1) constant social interaction and interruptions from other people and 2) bathroom time.

How many people these days have a dedicated home office, off limits to anyone else? How many partners sleep in different rooms?

Sure, perhaps the sensory experience plays some role, but if your bathroom is reliably the most interruption-free place for you, naturally you’d form a habit of catching up on all the “slow thinking”, most negatively impacted by interruptions, during shower.

I’ve seen people with interruption-free solo hobbies (be that hiking in the woods, motorcycling, rock climbing, etc.) describing similarly mindful experiences, but unlike those shower is the lowest common denominator and perhaps one that happens most routinely.