Why can't I use an email address for Two-Factor authentication on my Apple Account?

Realize that nobody here can provide the answer you want. We are just people like you. None of us work for Apple and Apple does not share its policy decisions with us (in fact we are not even supposed to ask questions like yours on this forum since it is one about policy and if Apple sees your question they may just decide to remove it entirely from the forum).

Account Security isn't just your concern. No service provider wants rogue accounts taken over by hackers. In as much as Apple gets to decide the conditions under which the accounts it provides can be used, my first reply was pretty much the answer to your question. Mac Jim ID's reply may help explain some of their reasoning.

It is possible to use Apple equipment without an account if you do not like the rules Apple imposes for use of an account.

I have an old iPhone that isn't signed into any account. I can use the basic apps. I can use it as a phone if I decided to set up cellular service on it. Of course you can't download special apps unless you live in Europe.

With computers, you could probably use a user account with access to apps purchased with another user account that does have an Apple Account associated with it.

I didn't say that you could use one to the same degree that you could use a device that was signed into an Apple Account. The extended capability is the user's decision, part of which is are you willing to accept an account on Apple's terms?

As for saving phone line cost, use the device with WiFi. I did for many years. I had several generations of older iPhones that I basically used as iPod Touchs. Of course then you have to learn about where you can get WiFi service, and for what. Many places still have free WiFi. It isn't secure but if somebody wants to watch me checking the weather forecast, I don't care.

As taught in most computer science classes, 2FA is:

• Something you know
• Something you have
• Something you are

You need 2 out of three of those for Two Factor Authentication and no 2 can be from the same category. Something you know is the Password/Passcode and your email account is just another account protected by a password, so having 2 of those does not qualify.

Something you have is a physical device such as a phone that can receive a verification code. Many companies also use security keys that would qualify for this factor.

Something you are is often referred to as biometric data. On the iPhone, biometric data can be changed with the Passcode/Password, so it does not qualify as a factor. Where it would apply is for access to a facility that also has a fingerprint or iris detector to go along with one of the other factors.

Each company specifies what to use for each factor to secure their accounts.

Why? Because Apple says so.

Nobody on this forum works for Apple so we don't know their reasoning any more than you do.

I always appreciate this explanation.