As it says on the title. Region_164 has the 'mixed' resource, allowing it to convert to a town, but it lacks any regional hidden resources, like numidia or libya or iberia, which control AOR units and, in this case, government type. The lack of any regional hidden resources prevents the Urban Administration government type (for Numidia) from being built, which in turn prevents large farms from being built. Large farms are required to convert the settlement into a city.
In addition, no units are recruitable there as well:
Spoiler Alert, click show to read:
(Governed Tribe allows you to train units based on AOR, provided it's in North Africa, Libya, or Arabia)





