Using HTML, CSS and Vanilla JS to resolving the rating system!

I just love to do this challange, it was really fun, I got a little better using vanilla JS, and I pround of it, but anyone can help me with one question? I got stuck in the first for looping, when I use a var instead of let the the result was aways 5, I just don't untertand this, if you know why please tell me, and feel free to any adivice for improve my code skills. Thanks!