And what happens when that email address is no longer available, it was a work assigned email? And the rescue email is my personal email that I still use, and the rescue email can't be entered in the box you displayed......
The email address used as an Apple ID identifier doesn't change unless
you change it, and Apple has no way of knowing you may, or may not still be using, or have access to that address. It would still be entered to say "this is the account in question," and administer the account.
Using email addresses as identifiers can lead to confusion, and not a great idea, following in the unintended footsteps of Social Security Numbers used as de facto credentials, but that's how the situation has developed.
When all else fails, the
Account Recovery process is the last resort, but not a sure bet to work.
Setting up online accounts is easy, probably too easy (based on the amount spam I get from the idiotic companies that don't require challenge responses during their signup process), but should be not be taken lightly.
That's why the credentials used to set up an account need to be carefully considered, not just in the moment, but also for the future, and safeguarded in your own records, and maintained to keep them current and valid.
Co-mingling work and personal credentials, and other computing activity, is also a bad idea, and can have unintended consequences; that's why many recommend against that practice.
As you're probably aware, what takes place on work-owned devices and computers is entirely within the employer's jurisdiction, which can be revoked at will, as the job itself can be. You may not be given time to update accounts which have credentials tied to the job you just left, or lost, and that's before considering whatever music, email, documents, accounts, etc., that reside on your work-issued equipment and is no longer in your hands.
Also, don't get me wrong, there are a lot of potential traps that exist due to these situations, and no service is perfect. These companies ask for a lot of information, and backup, to help them verify the account holder is genuine, but they can only go so far. Online accounts and cloud data is subject to a lot of terms and conditions people never bother to read, and should be viewed as potentially, as well as literally, ethereal.
These services are complementary to whatever they're really trying to sell, whether it's their product, or using you as their product, and offered under complimentary terms, with no direct upfront cost, or continuing subscription costs to the user. The companies bear significant costs to run these services, and have limits as to what they're willing to do to support free services that many consider perpetual, which they are not guaranteed to be.
For anyone who wants to say that the tech giants have become too powerful, profit hungry, and difficult to deal with, I would not be inclined to disagree. As an end user, one needs to look out for themselves, and really consider their relationship with them, and how to approach it.