- someone who gets anxious and blanks out given hardcore requirements these kind of interviews have, smart people can also go bad at tests
- someone who's having a tough day and would fare better taking the challenge home with quiet relaxing time like they would expect to have at work if they need to code complex algorithms
- no interest in past code written that could potentially show other traits of the candidate a quick coding quiz can't
- etc (no need to be extra creative here, just be humble and imagine what the candidate might be going through to get a dream job)
The simple fact an apparently smart young person joining the industry gets burned out like that due to stupidly arrogant hiring processes like these is a sign HR are failing miserably in the computer industry, and it's not something that started last month. Simplifying the burden of such process for actual people looking for a job to show how they are worth is dehumanizing.