2. Making an Argument: Why are they doing this to you?Professors assign argument essays, term papers, and similar writing projects to help teach you critical thinking because having those skills are a big part of what it means to be an educated person. In addition, employers depend on professors to prepare graduates who think critically.
One critical thinking skill is being able to present an argument to convince others. You're likely to have to make such arguments to yourself and others for the rest of your professional and personal life. You may need to convince others you are correct as you describe a thing, situation, or phenomenon. Or you may need to persuade them to take a particular action.
As defined by the National Council for Excellence in Critical Thinking, critical thinking is "the intellectually disciplined process of actively and skillfully conceptualizing, applying, analyzing, synthesizing, and/or evaluating information gathered by observation, experience, reflection, reasoning, or communicating as a guide to belief and action."
You'll find that definition (and more) at The Critical Thinking Community.
The discipline that has probably studied how to communicate in a persuasive way for the longest time is called rhetoric. Here's a short video about persuasive techniques that rhetoricians know work.
Undergraduates typically start learning about making an argument in GEC courses. But when essays, term papers, and other argument projects are assigned in your major courses, professors are letting you in on their game - teaching you how your own discipline looks at the world, what it finds important enough to measure and talk about, and what evidence it considers persuasive. In short, they are teaching you how to think critically within your own field.