>>95989187 (OP)Visual storytelling. Magic gems and crystals are used in a lot of fantasy settings as a tool for wizards to focus their magic through. And what's the easiest way to have it present at all times without keeping it in your pocket? Tied to a big stick so you know precisely where it is at all times. And what are commonly used sticks that are made to be sturdy enough for travel? Shepherd's crooks, which are obviously curved at the top to hook in sheep, or rigged to hold a crystal in so it doesn't fall out.
Basically, it's like that cause it gets the idea across of how important the wizard's power is, not to mention evoking the image of a royal scepter which are often ornamental staves with orbs on them to imply might and majesty.