School policies change. By initially relying on Prep Scholar to find out about the interview policy and not double checking the school website during application season, you missed an opportunity to interview.
If it was worth your time to apply, why wouldn’t it be worth your time to write an essay now when they have requested one from you?
Have you run the net price calculator for Case? Is it affordable for your family? Are you still interested in attending? If the answers are yes, you should write the essay.
Case is trying to protect their yield by determining if you are actually interested in attending if admitted. If you are having a hard time figuring out “Why Case?” that’s an indication you aren’t interested. If it isn’t a top choice for you, don’t write the essay. You are unlikely to get an offer below your EFC.