Just a desire to control this stuff probably. The WebKit browser choice is one of those super arbitrary things that Apple mostly does because it likes to be in

Just a desire to control this stuff probably. The WebKit browser choice is one of those super arbitrary things that Apple mostly does because it likes to be in control over what software manufacturers do. They'll argue some customer beneficial reasons for it, but it all just comes down to Apple wanting control; it's what permeates every component of their software ecosystem, especially on iDevices; they control app installs, they control what kinds of apps can and can't exist on the iDevices and so on and so forth. This is the company that famously recommended anyone who wanted to view NSFW content to "buy an Android"; it's safe to assume that the wish for control is the endgoal in and of itself, given Apples clear desire to play a byzantine morality police in other areas. Apple is the most textbook definition of a platform gatekeeper.