This one is hard to explain, simple to solve.

The Hard Part

They had a form, and one column they wanted to calculate the numbers. So they pulled those cells to another sheet. But that sheet didn't get the entire column.

The Solution

You use as the formula in the header, arrayformula or {} around the range of the column. Then any new entries to the form, will automatically come to the calculation sheet.

The Interesting Part

But the issue of why their initial solution didn't work, is super interesting.

Form responses inserts a new row for each submission.

So even if you enter your own data on the for responses page, the new submission won't overwrite them.

This isn't a bug, it's a feature.