Why do people take SANS courses that they already know?

In every in person, or live SANS course I have taken, there seems to be a few people that already know everything. They answer all the teachers leading questions, and they dominate the challenge at the end. Why?

I get it in college, you might be really interested in space, but you still need to take ASTRO101 because its required for your degree. But with cybersec certs, its not like that. If this person knows everything in 560 for example, …

courses cybersecurity people sans