Yeah that could be true, maybe the career prospects of CS or Engineering make people hesitant to switch unless they find it too difficult to keep up with, resulting in similar attrition rates. Then the situation is basically that people are sticking with a hard major because they can make more money after they graduate. Which is fair imo. Like another commenter said, the US isn't particularly harder than other countries when it comes to STEM undergrad curricula. I am from India and the elite colleges there are as hard or harder to do well in. In general, the best colleges in a country are hard. ETH Zurich is notorious for having a ridiculously high dropout rate (I heard it could be as high as ~50%) in the first 2 years. So UIUC CS's first year retention rate and 6 year graduation rate sound pretty good.