Put up a job posting on a job board and you'll get hundreds of applications. 90% of those you're going to throw out because the resume doesn't match the job description at all. What does that tell you about the candidate pool? It's an all out assault of candidate spam. You have to employ these sorts of basic filters to even get the number of interviews you do down to a managable number.
This is endemic to the point where applying only for jobs where you fit the job description is a losing strategy.
And even if your own job posting isn't one of those, how is the applicant supposed to know you're one of the few employers who actually means what's in the job description?
Most people who are smart and get things done will be capable of shipping code, if they can stay motivated. And that’s where having some signal about their interest can help. I want to know if people can inspire their teammates, not just get along, I want to know if they can lead by example, whether they’ll rise quickly, and whether they’ll love it for many years. The essential job functions are just plumbing, the important parts are more than that and aren’t demonstrated by evaluating for narrow, specific job skills.
Look, I don’t in a million years think grinding on Leetcode is some singular answer, or even particularly good. But I don’t see anything wrong with people who are interested doing it, and I also don’t see anything wrong with asking interview questions. I never put a huge weight on such algorithm questions, and there are a dozen other major interview categories. So there’s nothing wrong with asking a few algorithm theory questions, to see the bounds of what people know. I like getting into questions that people don’t know the answer to, whether it opens a conversation about what it means, or whether the candidate has no idea or doesn’t care, that is a small amount of useful signal to me.
I used to feel this way, but I think I’ve changed my mind. Interviews aren’t really primarily testing for skills you’ll use day to day, they’re testing for breadth of skills and knowledge and more importantly breadth of understanding. When I’m interviewing, knowing if the candidate has the specific skills for the job is the bare minimum needed to get in the door. I’m really more interested in potential, how much they can grow, and indicators of growth potential include how interested they are in the art of programming in it’s many different forms, whether it’s algorithms or math or software architecture, or coordinating people who write software. Puzzles are only the tiniest fraction of all that, but they’re still a signal that you like thinking about algorithms, and have exposure to different ways to write code and lots of algorithmic concepts.
A university CS degree isn’t particularly good at teaching job skills per se either, there isn’t much I use in my job day to day that I practiced in school, at a superficial level. But the school degree is pretty good at covering the broad concepts of computer science, and that has lasting value over the course of a software career.