In early days of this, I honestly think it was rooted in the famous Steve Jobs paranoia, the one that shipped without an app store and told users to use Safari, the same Steve Jobs that was said to not want certain medical devices during cancer treatment to touch him because they weren't beautifully designed. It was fundamentally about not wanting "dirty" things coming in contact with his "perfect" device. They dressed it up in language about security as a post hoc justification.

I remember in those days people would say they didn't want it to be like malware ridden Windows 98. But they omitted the weak security behind Windows at that time, which modern systems had long ago exceeded, even in the Windows world.