That would require Apple to give up total control of the software ecosystem, which they're not willing to do. iOS is their kingdom. This is another factor in play here. Apple could make devices "yours" and therefore un-hackable in this way, but to do that they'd have to surrender their own master key. Apple wants to keep their master key but not hand it over to the feds since they want a market reputation as the Swiss Bank of device vendors, so they have to go to the mat on this. If they lose either they lose the security/privacy crown or they lose the app store walled garden.
There are IMHO two reasons for Apple's platform fascism. The more self-interested one is that they want app store profits. The second more user-focused one is that they really want to keep iOS from turning into the shitware and malware disaster that Windows has become. On one hand Apple's walled garden keeps out certain forms of innovation and lets them dictate the terms, but on the other hand it lets them exclude trash like Superfish or Comodo's "security" junk.
There are IMHO two reasons for Apple's platform fascism. The more self-interested one is that they want app store profits. The second more user-focused one is that they really want to keep iOS from turning into the shitware and malware disaster that Windows has become. On one hand Apple's walled garden keeps out certain forms of innovation and lets them dictate the terms, but on the other hand it lets them exclude trash like Superfish or Comodo's "security" junk.