While I do get your point, the truth is usually somewhere in the middle, and I think that's the case here, as well. I'm not suggesting Apple should fix every single thing that anybody has a concern with, but it would be good if they were more open about what they're not fixing and why. "Security through obscurity" doesn't work, and there's no good reason to not be open and communicative about this stuff.
What I’ve described in this case IS the middle, though. On one end, Apple does nothing, on the other Apple drops everything to fix the “installed app on device” exploit. The boring mundane reality based middle is that there are
definitely exploits that exist that are more serious than this, exploits that don’t require you
1. Obtain a developer account, with your personal credentials
2. Pay the $99 using your personal/business funds
3. Develop an app that’s able to be allowed on the app store
4. Submit a few successful releases with no exploits so the review process may get lighter? Maybe?
5. Submit the release with the exploit hoping that it’s not found, BUT if it is, it’ll be removed from the store, undoing all your work from steps 1 thru 4.
In the middle, you use your OS developers to focus on exploits that require no interaction from the user and use or App Store developers to create patterns to search for and help find apps that may be doing this OR might try to do it in the future. Then, when there’s opportunity, you have the OS developers make the redundant change on the OS side.
And, obscurity is a primary part of security. I get where the phrase comes from (and folks tend to gravitate towards the ones that rhyme

), but a big part of any security posture will always be “There’s some information about this that’s not going to be publicly available” or obscured. We all know how house access works, via some form of locking mechanism with a unlocking device that matches it. The ONLY thing keeping us from easily entering any house we want is that the keys are obscured. Now, if you were to send an email to everyone you know saying, “In order to be open and communicative, I’d like for everyone to know that the key I kept under the flower pot has now been moved under the mat because I got tired of moving that pot,” well, it’s definitely more open and more communicative for sure!