I just like doing cool things, honestly. And I know a few people that are just like me.
Heck, I passed a harder version of the test (including the theory, I'm a senior/lead/old-fart so I was expected to implement everything on top of the discussions) and I left formal education at 17 :)
They don't have to implement a working version, just give a good outline and be able to answer questions about it :)
For experienced people we go further, and do ask for some coding.
You've got 5 years experience in SQL? Then solve this simple problem which requires using JOINs and aggregates.
You're a javascript expert? Great, then demonstrate that you know the syntax and know what a closure is.
Java expert with a focus on patterns? Then you should be able to implement one of: Singleton/Factory/Command.
We get more people who have 10 years of experience with C# are are self proclaimed experts, but who don't know the difference between the heap and the stack then we do CS students applying for the wrong job.. but that's for a different thread :)
But I love discussions too, and if it's something I'm comfortable with, I could keep talking about the topic for as long as the interviewer wants.
I think there's value in recognizing when you don't know the answer to something. I had an interviewer ask me the difference between call and apply in JavaScript, at the time I wasn't sure, so I started to answer him... I explain that I knew you could use both to set the context in which the function was called, but eventually I just said: I'm not sure. And the interviewer gladly explained it to me.
In my case I got an internship where they gave me a 24 hour project to demonstrate my skills. I found that way less stressful than any interview I've ever had. And after the internship the company was so happy that they offered me a full time job!
Unless that knowledge is something vital and general. I.e. like not knowing what HTML is.
In the future I want to use internships to find younger engineers - it lets you get to know people a bit, and keeps new ideas flowing through the company.
A developer who writes an implementation of the quicksort algorithm as part of their job should usually be removed from their post for incompetence.
The interview process should be a two-way procedure which also allows the candidate to understand what is expected of them in a role (and make their decision about the job accordingly). If regurgitating quicksort is expected, then this is a fair test: otherwise, this is not how you should be presenting the job.
Thankfully I got an internship that let me do a small project to demo my skills, instead of hazing me. And after my internship they were so happy that they offered me a full time job.
It is stress. Introverts like myself I imagine collectively are horrible under intense pressure from random strangers who can dictate your future for months or years.