Indian dairy sweets are written around milk as it is sold in India, and US supermarket milk differs in several processing details. Those details show up directly in the pan.
Fat content is the first mismatch
Recipes generally assume buffalo milk or a rich cow milk with a high fat content, both considerably richer than standard American whole milk.
Lower fat means less richness in the finished sweet and a lower yield, since the fat is a large part of what remains after water leaves the pan.
Cooks compensate by adding cream, using half and half for part of the volume, or accepting a leaner result and adjusting expectations accordingly.
Homogenization changes how the milk splits
Homogenization breaks fat globules into small particles suspended evenly through the milk so that cream cannot separate out and rise.
When acid is added to split the milk, those dispersed fat particles are held less tightly in the curd, so more fat escapes with the whey.
The practical result is a slightly drier, less rich curd than the recipe assumes, and a whey that looks cloudy rather than clear yellow-green.
Ultra-pasteurized milk resists setting altogether
Milk heated to very high temperatures denatures its whey proteins, and those altered proteins behave differently when acid or culture is introduced.
Curd set from ultra-pasteurized milk is often soft and slack, and cheese-making from it can produce a weak, fragile curd or none at all.
Ordinary pasteurized whole milk works far better, and the distinction is printed on the carton, usually as UHT or ultra-pasteurized near the fat percentage.
Reduction times do not transfer
A recipe's stated reduction time assumes a particular pan, a particular flame and a particular starting milk, none of which match automatically.
The usable instruction is the visual endpoint rather than the clock: a coating thickness, a color, or the point where the mass leaves the side of the pan.
Cooks who work to the described appearance instead of the stated duration get consistent results across very different equipment.
Milk powder is a legitimate shortcut, with caveats
Full-fat milk powder reconstituted into a paste behaves close to reduced milk in many sweets and saves a long stretch at the stove.
What it lacks is the browning that develops during a real reduction, so the flavor is milder and the color paler than the traditional version.
Nonfat powder, which is what most US supermarkets stock, compounds the fat problem and generally needs ghee or cream added to give a workable result.