I can't log onto my Apple iCloud account on my Mac because I have an old iPhone which I don't remember the passcode to. Why isn't the Apple ID password enough? I don't want to erase my iPhone data just yet.

I have always been able to log onto my Apple iCloud account on my iPhone, though I have now forgotten the passcode to the phone itself. Now that I bought a Mac, I cannot log onto the same Apple iCloud account unless I agree to erase everything on my iPhone. Shouldn't the Apple ID password grant me the rights to everything regarding my Apple ID regardless of which devices I can't remember the passwords for?