Now that @twitter has had a minor password scare, will they finally allow time-based TFA to be turned on without requiring that the user provide their telephone number? I still have no idea why you would ever want to disincentivize users from using TFA :/
No, they don't - you can make as many accounts as you want without worrying about having multiple phone numbers. It's only if you want TFA that you need multiple phone numbers, which is nuts!