The Wizards' Guild provides free schooling in a magical lore principally as a means of providing social structure and order. They like being paid for spells but are not dependent on that source of income. They like wizards not to undercut them and they don;t officially like wizards teaching rogues spells but they accept that it is going to happen.
They like the Rogues' Guild because it brings order to those not in the Wizards' Guild who can do magic. They like control over rogues.
Recently in Khaboom, the Wizards' Guild backed the incumbent Mayor in his re-election campaign in return for him not interfering when they bought out the Rogues' Guild. Now the Wizards' Guild has subsidiary and pretty much a monopoly on magic in the city. The hold the equity and the membership fees the Rogues' Guild receives flows on to their coffers and they have the final say in Rogues' Guild regulations and bye-laws.