Many people fail fizzbuzz. Most interview questions at big tech are not much harder than fizzbuzz. You are not qualified to be a software engineer if you can't write fizzbuzz after seeing it for the first time in your life.
Similarly, if I ask you "write a program in your language of choice that prints all even numbers from 1 to 100", you can either cry about it or take the 3 minutes and actually do it. If you can't, it's a pretty clear signal that you don't actually write code in your day job and aren't suited for this one.
This is why we have leetcode and Fizzbuzz. There are simply too many phonies applying and counting on their charm and charisma to get them the job, which sometimes works when you don't make candidates actually demonstrate their skills.