Why do some teachers think that a ton of negative, public feedback is going to help students learn?

Here’s the deal. I am 35 years old and a full-time student. I’m learning Spanish because I’m moving to Bogotá in August. Most days I absolutely love putting in the hard work that is learning another language. I’m in class for five hours a day and then put in an additional three+ hours of independent study in the computer lab. I put my notebook on my kitchen counter and review words while I’m eating breakfast, cleaning the house and feeding my son. I complete grammar exercises while I’m eating lunch. I review words before I go to bed every night. It’s hard, but it’s exciting.
Yesterday we had a guest teacher who completely tore me apart in front of my classmates and said the only way I will improve is if I do more than I am already doing. It made me want to RUN from Spanish. I left campus during lunch and did not look at another Spanish word for the rest of the day.
It is true that I overreacted to her behavior. But it is also true that the brain hates stress. One of John Medina’s Brain Rules is: Feeling safe enables learning. He says it’s the brain’s primary concern. Why is that so hard to understand?
I guess the silver lining in my situation is that now I really do know how kids feel when a teacher tears them down, especially in front of their peers. Everyone reacts differently to stress, but this teacher’s feedback was so discouraging that it made this learner want to study less.
Luckily my regular teacher is super kind and encouraging. She’s tough, and points out my errors, which is essential, but she mixes that with a healthy dose of positivity.
I wish all teachers could be like her.