At our selective school there are many more students who want to do research than there a professors to work with. It stands to reason that if each professor gets only one student then the number of positions is small and fill up quickly.
There are plenty of kids at elite colleges who test well. That doesn’t make them innovative, ambitious, or the smartest people in the room. I see their grades and I talk with them every day. The “best and the brightest”? No. They’re great kids. But there’s a lot of hand holding. It’s not difficult to do reasonably well when you’re not allowed to fail.
But college can be a very different world than high school. There are open ended questions with no one right answer that test how students think, not just how well they memorize. Some really struggle with it, some do okay, and a few excel. This is no different than our state school.