The vm has "tools" preloaded and helps students experiment with configurations that don't end up causing the host computer to be badly configured. The host PCs are pretty restrictive and have no admin privileges. The VM is fully capable of being "free to mess with" in a sense. The idea behind it is to prevent unauthorized bad actions on the host pc. Creating a separation of students' abilities behind a vm. You can use your own PC, but that is cumbersome and unnecessary. The "forced to" is a bit loose, but it helps students start from a state where the teacher can help guide the students to what to do.