WHY DO WE SPEAK FLUENTLY WHEN ALONE BUT STUTTER IN PUBLIC?

WHY DO WE SPEAK FLUENTLY WHEN ALONE BUT STUTTER IN PUBLIC? This question has intrigued me for a long time. Recently, I read a research on this. The research stated that out of 1485 Russian speaking people, 65.66% (975 people) did not stutter alone; 27.47% (407 people) stuttered significantly less; 5.25% (78 people) stuttered as usual. The numbers for English speaking people were similar. So, it is safe to say that this is a common theme across all the people who stutter. But why does this happen? First thought goes towards the fact that it is bcoz of fear of getting laughed at / fear of embarrassment by other people. But I don't think it is that simple. I also stutter when I talk to Siri or Alexa. My theory is that it happens due to us hurrying to say what we have to. We fear that we won't be able to speak in normal time. So, that makes us hurry, which makes us anxious, which makes us stutter. Please share ur thoughts on this. Would love to know different POVs & experiences.