Why am I doing this?

The main point of these weekly reports is to assist you in uncovering and correcting any problems you are having in this class. It is the instructor's role to provide you with performance evaluations in the form of tests and graded assignments. However, the person best situated to identify your successes and failings in this course (and their causes) is not the instructor but yourself. If you make this process of introspection a routine aspect of your efforts through the week in this course, you can make timely mid-course corrections. You won't have to wait weeks until you take the next exam.
A secondary purpose of this form is to encourage you to communicate with me regularly about my efforts in the class. Timeliness matters here, too. If I were only read your reactions to the course on the official evaluation form after the semester ends, then nothing you would write could improve your semester's version of the course. In that situation, your incentives to provide useful (but costly in terms of your time) feedback are limited.