Take for example a university. Many of them seem to use Duo[1], which is not something you can replace with Google Authenticator or other TOTP app. They require it for students as well as faculty and staff. Is it reasonable for them to have to provide a device to all those people, forcing them to carry two devices around, and then also deal with replacing lost or broken devices? The cost of this would simply be added to the technology fee that students have to pay, when they all already have smartphones and could use the app for no additional cost.

[1] https://duo.com/