You're just thinking of security -- and there are many valid concerns around using SMS-based cleartext messages as a 2nd factor. But additionally, a big issue

You're just thinking of security -- and there are many valid concerns around using SMS-based cleartext messages as a 2nd factor. But additionally, a big issue is reliability of the 2FA mechanism. Especially when your service provider is overseas, or you're roaming, the SMSes may simply not arrive in time.