For the record, I'm in favor of legal mandate that hardware owners have the buy-time option to enable adding their own keys to any root trust stores on their devices. However, that'd be in addition to Apple's keys and wouldn't be about the security of Apple's keys, because Apple is part of the fundamental trust foundation if you buy a Mac or iDevice. Period. The devices are massively vertically integrated, right down to the core silicon which is completely custom. Apple has absolutely unfettered ultimate low level access opportunity up and down the stack. If you completely don't trust Apple, then you absolutely should not use their hardware at all. So some level "trust Apple" is simply a security axiom on this platform.
And they've shown that to be not unreasonable at least when it comes something like root private keys. Fact is they've been operating for a long time now and like the rest of the big players that hasn't been a leak issue. It's not that big a deal for a big player to physically secure such things to a high enough degree that it's unlikely to be a limiting factor. Dedicated rooms, full offline, hardware backed Shamir's secret sharing for m-of-n key signing ritual requirements etc etc.
And they've shown that to be not unreasonable at least when it comes something like root private keys. Fact is they've been operating for a long time now and like the rest of the big players that hasn't been a leak issue. It's not that big a deal for a big player to physically secure such things to a high enough degree that it's unlikely to be a limiting factor. Dedicated rooms, full offline, hardware backed Shamir's secret sharing for m-of-n key signing ritual requirements etc etc.