It’s cause when you’re talking in conversation you have the luxury of switching words around and all that. When you’re reading out loud everyone sees the same words you do if they’re following along. It puts pressure on saying every word perfect because you can’t switch out a word for a different synonym. Like jobs that require you to answer a phone call an exact way. I’ll stumble on that for days, but if I have the freedom to switch around the introduction a little bit I’m fine