Omission of caps from pattern drafting manuals

While looking at men's pattern drafting manuals (I do not know if it is different with women's patterns), both recent and historical , I noticed that they rarely or never discuss patterns for caps. If I am correct with this observation: Why was and is this the case? Is it traditional for caps to be made by hatmakers rather than by tailors, even if their construction is arguably more similar to making a coat or trousers than making a felt or straw hat?