me giving, let's say, twitch my phone number gives them exactly 0 ways of tracking me in any way whatsoever

Source: worked for a mobile company

First part is not quite true, varies by country.

Second part is full on Olympic mental gymnastics

yeah, no idea why you're getting downvoted, it's clear why companies are so eagerly embracing and requiring 2FA -- if the benefits were only for the consumers, it wouldn't be mandated anywhere near this quickly. but when they know they get a real human phone tied to every account, that's a huge motivation