Apple ID Two Factor Authentication is Flawed

Could someone tell me why Apple use Trusted Phone numbers for 2FA instead of a Third Party or Apple’s Own 2FA token generation App (If they create one). Because Trusted phone numbers can be dangerous, think of a situation where a user has only one iPhone and one Phone Number, the person set the same phone number as Trusted number. In case the user’s phone is lost or stolen then the person who finds it or steals it can easily recover the apple account and activate the phone using the Phone Number because the Sim Card is inside the phone and the Sim card can be inserted in another phone to receive OTP.

This is just a stupid implementation.