Not so much intelligence but applied diligence on top of intelligence is my sense. If you want what they’re offering and don’t want to jump through their hoops for it then they don’t want you. For those that ball at the hoop jumping as being beneath them, there’s probably additional characteristics that comes with that that they’re trying to filter out.

Given that many job applicants apparently can't write a Fizz-Buzz implementation, I'd say that being able to implement an algorithm is probably a reasonable way to cull the herd by a hefty margin.

https://blog.codinghorror.com/why-cant-programmers-program/

There's a correlation between the belief that memorizing algorithms correlates with intelligence and the application of algorithm questions in interviews.