Earlier quoted context omitted.
Yes there is. I don't want Facebook or Google to move all their apps to side loading or an alternate store with lax controls and opaque privacy disclosure. I need to use their apps, but I want them to have to satisfy Apple's app store policies. Side landing and alternate stores would cripple the effectiveness of those policies.
So the reasoning is "if you allow my phone to be unlocked, so many people will want alternate stores that Facebook and Google will unlist their apps from the App Store and use the alternative stores only, and then they won't be as rigorously reviewed"? Like how you can't get Facebook on the Play Store because it's only available on F-droid on Android, for example? That's certainly... interesting.
Facebook is quite happy on the Play Store because it has weak privacy and disclosure policies, because Google has no interest in enforcing such things.