Because having salt of an acid out of a citric fruit in water, makes it tasty.
I just use some black salt, though. Much cheaper.

It's not dumb in the sense that water that is not alkaline is not the same as water that is alkaline with some added acid.

In Eastern Europe the soft drink created by mixing sodium bicarbonate into water and then adding a tea spoon of lemon juice or vinegar to it was an oft used refreshment before the 80s.

Mixing sodium bicarbonate into water, even with just a teaspoon of acid like vinegar or lemon juice added, is still a good antacid.