That was because they were a single stage pain with no lacquer over the top. These days, their generally base coat and lacquer so don't fade in the same way. There are some who still use single stage mind you, but not loads.Thinking about it depending on the paints and paint finish and especially with red. Lots of uv light/sunlight candidates fade/send it milky too.
Vauxhall red (pink) anyone... Old royal mail vans. That can be cut off until you use all the paint up.