Reduced milk, fresh cheese and set dairy form the backbone of Indian sweets. Very few other cuisines built their desserts this way, and the exceptions cluster in predictable places.
Dairy surplus is the first requirement
Turning milk into sweets consumes a lot of it, since most of the volume is water that gets driven off. That demands a surplus beyond drinking and cooking needs.
Regions with large dairy herds and a cultural preference for milk over meat production had that surplus available, and South Asia is the clearest example.
Elsewhere, milk was more often turned into aged cheese or butter, both of which store and trade better than any fresh dairy preparation.
Aging was the alternative that most cuisines chose
European dairy traditions solved the preservation problem with rennet-set, aged cheese, which keeps for months and concentrates milk without continuous fuel input.
Indian dairy took the acid-set and reduction routes instead, both of which give products that are used within days rather than matured.
Those are two different answers to the same problem, and each shaped the sweets that came after it: cheesecakes and custards on one side, chhena and khoya sweets on the other.
Eggs displaced dairy as the structural ingredient
Where eggs were plentiful, desserts used them for setting and aeration, since a custard or a sponge achieves structure with far less raw material than a milk reduction.
Indian sweets, developed within largely vegetarian dietary frameworks, could not lean on eggs, so dairy protein and sugar crystallization took over those structural jobs.
That constraint explains why so much Indian sweet technique is about controlling protein and crystal texture rather than about foams and batters.
Fuel economics discouraged long reductions
Reducing milk for hours is expensive wherever fuel is scarce or costly, which pushed many cuisines toward desserts that cook quickly or not at all.
South Asian sweet-making concentrated in specialist shops partly for this reason, since one large vessel over one fire serves a whole neighborhood.
The trade persists in professional structure today, which is why these sweets are still bought more often than made even where fuel is no longer the constraint.
The exceptions prove the pattern
Milk-reduction desserts do appear elsewhere, notably in Latin America with dulce de leche and in parts of the Middle East with milk puddings and cheese-based pastries.
Each of those regions had both a dairy surplus and a sugar supply, which is the combination the technique requires.
Where either was missing, sweets were built on grain, nuts, honey or fruit instead, and the resulting desserts look nothing alike despite serving the same purpose.