Everyone knows that two factors are better than one. My problem is that often the only second factor allowed is text messages sent to your mobile phone. This creates two concerns:
I travel frequently overseas and lose access to 2FA accounts any time the associated SIM card can't touch a network.
Your phone is inherently your least secured device. I install way more software and download way more files on my phone than anywhere else with much less ability to verify sources or control access. For example, nearly every app requests sweeping permissions to function correctly. Even apps that aren't granted explicit permissions have been found to backdoor those permissions through google services.
I feel like linking my phone to sensitive accounts (such as banking) would actually make them more exposed to attack and more difficult to maintain legitimate access.