Humans are in the majority. The Lords of the principalities are all human, as is the civil service. They hold the strings of power and have no intention of letting them go.
Around 1 in 5,000 humans will express magic. Mages are comparatively rare and are valued accordingly. A mage need never starve.
Mages can be born to any family, but they are more common among the nobility. Mages born to non-noble families are often fostered out. Slavery is illegal in Reyern but it is not unknown for mages from very poor families to take on a period of ‘indenture’ to one of the Towers to pay for their training.