[Peter von Kleinsmid]

Such details vary by GM. If you have a PC who knows the Staff spell, ask your GM about the details the PC knows. If you have a PC who doesn't have that much knowledge, you could play out having your PC talk to a wizard in the game world about it.

Your last question seems to be missing a word. If you just mean why doesn't everyone with a dagger instead carry a main-gauche... they cost twice as much, are larger, heavier, more conspicuous, and only some people would ever choose to use them that way (so they're also pretty uncommon in some places/campaigns).