Engineers: Why isn't a roll pin lock used universally for linking to a motor shaft?

I’m trying to understand why so many motors come without a pre-drilled hole in the shaft for a pin to lock into. Some are D shafts and some are just round. It seems weird that they would make them without holes by default. Obviously there must be a reason. Is it cost? or is there a significant structural penalty for making such a hole? something else?