“Builders’ Paint” is any low-quality, poorly-applied paint (either outside or inside) that fails to hold up. Usually in the very dull gray and tan families, it is favored by Kansas City rehabbers and new construction builders.
Poor quality paint can’t really be “fixed”, only covered by a better product. And a better product means it will hold up to the bumps and bruises of daily life.
Builders paint is used because it costs less. It costs less because, very simply, there is more water in the can and less “stuff”. So, when it dries there is a much thinner and less-durable film of paint.