This is a nightmare for students that don't think on their feet.

Can you explain why? As I understand it, you're supposed to be able to talk about the work in which you already invested the mental energy to write. Writing involves much more "brain work" than speaking, so if you've truly written the work in question, you should be capable of speaking about it -- unless you have some sort of disability, in which case, there are probably alternative avenues.

Part of college is growing as a human, and part of that is social interaction.

For the same reason a lot of universities in Europe require you to take philosophy. It's completely unrelated to C++ or data-structures, but it adds to your acumen as a whole.

Not that different from some universities that require you to be able to swim[0].

[0]: https://perec.columbia.edu/swim-test-requirement

This is definitely something you can't force onto students on a whim. This is a something that can be taught and worked up to though.

Yeah as much as I like the idea, I know there will be some brilliant and driven students who would have a hard time with this due to temperament. For me, if I’m excited about something, I can talk for hours. Maybe not so for everyone though. Then again, not all brilliant and driven students test well either, so… pick your poison?

If you don't have enough of a mastery over a subject to rapidly respond, maybe you are not fit to pass exam certifying your mastery over a subject.