Nonstick coatings look like the obvious answer to milk sticking to a pan. In practice they make milk reduction slower, riskier and shorter-lived, for three separate reasons.
The coating sits on a thin, light base
Nonstick pans are typically built on thin aluminum, because the coating is applied to a lightweight body and thick construction defeats the price point.
Thin metal develops hot spots directly over the burner, and milk solids settling on those spots scorch before the surrounding liquid has evaporated.
Heavy pans work better precisely because mass evens the heat out, spreading the energy across the base instead of concentrating it where the flame touches.
Reduction is a scraping process
As milk reduces, a skin of concentrated solids forms on the base and the walls. That skin has to be scraped back into the liquid continuously.
Scraped in, it dissolves and contributes the browned flavor the process is partly for. Left in place, it burns and taints the entire batch.
Doing that properly needs a metal edge and real pressure, both of which damage nonstick coatings and shorten the pan's life considerably.
Nonstick discourages the heat the job requires
Manufacturers advise keeping nonstick cookware at moderate temperatures, since coatings degrade when overheated, particularly if a pan is left empty on a burner.
Milk reduction is a long process, and cooks are tempted to push the heat to shorten it, which is exactly what the coating is not intended for.
Following the manufacturer's temperature guidance is the right call, which in practice means the pan is unsuited to the technique rather than that the guidance should be ignored.
Surface area matters more than sticking
Evaporation happens at the surface, so a wide, shallow pan reduces far faster than a tall narrow one holding the same volume.
Most nonstick pans in a home kitchen are skillets sized for a portion or two, and a milk reduction quickly outgrows them.
A wide stainless or heavy-clad saute pan gives both the surface area and the mass, and the sticking it allows is the part the cook is supposed to manage.
What to use instead in an American kitchen
A heavy-bottomed stainless steel pan, a clad saucier or an enameled cast iron pot all provide the thermal mass this needs and tolerate metal utensils.
The traditional answer is a thick brass or heavy tinned vessel, and the reasoning behind it is the same one that makes clad stainless the practical modern choice.
Either way the technique is unchanged: moderate heat, constant movement, and a flat-edged spatula that reaches the corner where the base meets the wall.