Evolutionarily speaking, it is easy to explain why nearly all beings – regardless of species – seem to so enjoy a good soak.
Primordial soup.
Soaking is so relaxing. You can just settle in. Take a load off. Luxuriate.
But where in the past you had to share the soup pot (so to speak) with every other life form on the planet, today you can have your spa day and your solitude too.
Just make sure your personal bath is sized perfectly for one.
And only one.

Pearl, Malti, Bruce & their mama