Thinned, salted yoghurt drinks appear across hot regions that share no culinary history. The convergence follows from what the drink does in heat rather than from any exchange between them.
Salt is the part that matters in heat
Sweat carries dissolved salts as well as water, so replacing only water leaves the balance of the two further apart than before.
A salted drink returns both together, which is why the savoury versions of these preparations are the ones that persist as everyday drinks rather than as treats.
Sweet versions exist alongside them, but they occupy a different role, closer to a light meal than to something drunk during the working part of the day.
Fermentation makes milk keep in the heat
Fresh milk spoils rapidly at high ambient temperature, which historically limited how far it could travel and how long it could be held.
Souring it deliberately lowers the pH enough to suppress the organisms that cause spoilage, extending its usable life considerably without refrigeration.
Thinning the result with water then stretches a small quantity of milk across a household, which mattered where dairy was valuable and the climate was against storing it.
Diluted yoghurt is easier to drink in quantity
Appetite and thirst both fall in heat, and thick or rich drinks become unappealing well before the body has taken in enough fluid.
Thinning reduces the fat and solids per mouthful, so a large volume can be drunk comfortably where the same amount of milk could not.
Acidity also stimulates salivation, which makes the drink feel refreshing in a way that plain water does not once someone is properly hot.
Aromatics are chosen for their cooling impression
Cumin, mint, coriander, ginger and curry leaf recur across these traditions, and they share a bright, volatile character rather than a heavy one.
Some of these compounds act on the same nerve receptors that respond to temperature, producing a sensation of coolness that has no thermal basis.
The perception matters practically, since a drink that feels cooling is drunk more readily than one that is merely cold.
The format tolerates whatever is available
The drink can be made from any soured dairy, at any dilution, with whatever aromatics a household has, and it still works.
That flexibility is why the same idea appears in so many places with different names, different textures and different degrees of thickness.
It also means the preparation survives changes in supply, since nothing about it depends on a specific ingredient being on hand.