Are we sure this is not just harmless and arbitrary information being parroted? Do we have verifiable sources other that anecdote? I find it hard to believe that there is just a single value for water intake across the massive biological spectrum that is humanity and expect to see a range when this conversation comes up. You're also getting water from foods, which I am sure is not being accounted for. Reminds me of the 10k steps a day that just happened to be "correct enough" to be believed and acted on. The truth is much more nuanced and depends on a number of factors in a person's physical health.

Without concrete verifiable findings, the best we can do is learn to pay attention to our bodies and drink maybe a little bit more water than we think we need to.