it might well be that your hammer is very old and/or crappy and made of soft steel and so the head has rounded over and mushroomed and nobody thought to file or grind it flat again.
My good quality CrVa hammer has a FLAT head because I keep it that way.
BTW you can drill pilot holes for nails in hard woods or where you cannot afford to bend one. Been there, done that.
And I'm just a home woodworker. But my father was an engineer and taught me the proper respect for a good tool.