When you're taking a self-portrait it's easier to hold a phone vertically one-handed, your self image fits the screen better, and your followers are going to vi

When you're taking a self-portrait it's easier to hold a phone vertically one-handed, your self image fits the screen better, and your followers are going to view it in portrait mode on TikTok anyway. When you go yo take a selfie of something other than your face, you just keep the habit.