While there are some kings with a bit of Wizardry, Wizards as a general rule are not rulers.
There are several reasons
#1 They are scare
#2 They lack the skills and temperament for the most part
#3 Ruling takes away time from developing magic which is more important to most of them
#4 Many people won't follow them
The Return of Planescape? - Curious. There is a brief note on this 'countdown' at Enworld.
13 hours ago