Google Authenticator is pretty easy to use, as are the alternatives. Also really easy to provision. Not sure how SMS is more practical than an offline code generator.
First notice how "pretty easy" isn't the same as straightforward. Good luck getting my mom to figure it out.
If you lose your phone, upgrade to a new one, or erase and restore it you lose all your authenticator credentials. That doesn't happen with SMS.
If you're in a situation where security is paramount, then physical cards or authenticator are a better way to go. If you're 99.9% of the population, Sms is a far better solution.