The argument then goes back to, why pick up an external dependency and cost for open standard authenticator when you could just include a library and generate it yourself.
This allows a developer to have all the benefit of the Authy API, including enhancing the experience using push authentication or dropping back to SMS if needed, as well as allowing users to use an authenticator app of their choice. It's the best of all worlds in this case.
But if building and maintaining app based TOTP using a library is good enough for you, then go for it. I'm certainly not going to make you use Twilio's APIs, but plenty of businesses do see the benefit.
