It’s surprising to me that someone could know what a for loop is but not summation notation. Is summation notation not taught in school?

You have to learn about summation before you learn calculus, because any definition of integration requires series.

Imagine the idea being used for more complex math operations. Summation/Product notation is pretty straight forward (if you were ever taught it). The vast majority of math notation is not. Or rather most people are not taught most math notation. And even if you were taught it it's really hard to remember!

Freya's content around math is always incredible, and yeah that's exactly what I meant.