I can't remember how they felt to handle -if and when I ever used one.
Seeing a picture of one recently has prompted me to ask: Does anyone
know why they are such an odd shape?

Hardly the ultimate coefficient of epic ergonomics are they.
*
*
*
*
*
*
*
*
*

(Coefficient: numerical measure of a physical property.
Ergonomics: the applied science of equipment design.)

Weatherlawyer wrote:

Does anyone know why they are such an odd shape?

If you're talking about a boilermaker's caulking hammer, then it's a
wooden mallet rather than a hammer, because it's used to drive a
caulking chisel. The shape is very long and thin to get access to
small areas. As it also needs a fair bit of mass behind it, then the
ends are usually ringed with iron hoops. These also reduce splitting on
the faces. The length of the head isn't a problem because caulking
chisels are short.