iOS is one of the world's 3 most important COTS platform targets, along with Chrome and (guessing?) Windows. Localhost privilege escalation on iOS can be a a link in a drive-by jailbreak chain.

iOS has universal inter-app sandboxing. macOS is getting there, but not quite yet. So on iOS, a privilege escalation vulnerability is useful for getting data out of a different unprivileged context; on macOS, you might already be in that context.

It’s a big and hard-to-exploit target?