So, I haven't applied to MIT (lol). But some schools I applied to did ask what major I'd like to do. It could be that MIT doesn't accept applicants who want to do CS who haven't taken some level of CS fundamentals before.
My school wasn't that mean. I think the programming II class was the weed class, and I think the deciding factor was that the projects just took a lot more time than homework you're likely to get in other 100 level courses. I had no CS background but with enough time I got through the homework. Not everyone had the time or the interest.
It's been a while since I graduated but for those wanting a high demand major from a dept with limited resources, it seemed normal for one of the 100 level courses to be a step up in difficulty. Pushed out a lot of people from pursuing CS at my school.
Other schools make you apply to the major, and that process just weeds out those the dept thinks are not suited for the program.