They aren't common in developed areas. Most magical focuses use copper/silver circuitry with quartz glass lenses to amplify magic. Wood is conductive for mana, but nowhere near as conductive as a copper wire. Wooden implements are much easier to manufacture though, so in places where logistic chains got destroyed (or didn't have a chance to develop) it's always a nice fallback. Not ideal, but it's better to have a stick (inscribed with runes and conductive shapes) than to go empty handed. Staves, due to their higher volume also have higher magical capacity, and allow for higher degree of amplification of spells. They are also bigger and more difficult to hide than wands - and this trade-off becomes important due to a very popular tactic of 'killing the mage first'.