You probably have an "unlimited voice and text" account for your phone. Twitter doesn't. It pays for what it uses, and it uses a lot. Some of that money goes to phone company scammers who have bots send bazillions of fake SMS authentication requests and rake in the text messaging fees.
Saving $60 million a year is good for Twitter, whether it increases new revenue from Twitter Blue subscriptions or not.
The added security of using an app or physical key instead of trusting a more vulnerable authentication method is good for you.
And those predisposed to cry over nothingburgers get a new one to cry about.
Everybody wins!
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