It's not like the clans tolerate, but who wants to fight a clan of self isolated powerful mages (similar to the elemental clan in power) living in floating castles?
Not all powers of the Scorching Hell are under the influence/command of the Queen. They have other allies to call, and they can just as easily fly to another location, since they claim no domain over any territory of the scorching hell.
If a clan risks fighting against them, they might risk weakening themselves and open an opportunity for another clan to backstab them.
+ They do have neutral relationships with the queen. They are known to be excellent traders, and they supplies the queen with artefacts/materials that she might require.