The reason why Breyers does not melt like traditional ice cream melts is because Breyers is now a Frozen Dairy Dessert and not true ice cream anymore due to lower milkfat content and higher amounts of corn syrup as well as air stabilizers and emulsifiers, which resist melting for better texture and shelf stability.
The reason why Breyers is no longer called ice cream is because many of Breyers products have changed their formulas and are now using cheaper ingredients like thickeners, corn syrup and more air, (overrun), which caused Breyers ice cream products to no longer meet the FDAs legal definition for ice cream.
For the FDA's legal definition of ice cream to be met, the ice cream requires at least 10% milkfat and if the ice cream product contains less than 10% milkfat it's required to be labeled as a Frozen Dairy Dessert instead of ice cream.
The shift in ingredients changing in Breyers and Breyers no longer being called ice cream was initiated by Unilever, which aimed for a smoother and cheaper to produce product, although many people felt that it tasted different and didn't melt like traditional ice cream.
Breyers began using ingredients like corn syrup, gums like guar gum, carrageenan and tara gum as well as more air which reduced reliance on expensive cream and milkfat.
The new recipes of Breyers were also designed to create a smoother texture and reduce cost of production, but the added stabilizers also made them melt slower.
To be legally called ice cream in the United States, the ice cream product must meet specific requirements, which include using a minimum of 10% milkfat and a certain weight per gallon.
Any ice cream products that fall short on these standards, must instead be labeled as Frozen Dairy Desserts and not ice cream, which is a change that became common for many varieties of Breyers ice cream around the year 2013.
Although some Breyers products are still ice cream, but others, especially the Breyers in the blue containers are frozen dairy desserts with different ingredients.