The most important thing to getting an interview is networking. This goes for really any job, not just development work. Development skill is pretty important too, but when your looking for a job, employers usually look at a lot more than just that.
As you already said, these sites are great for practicing your skills. But who cares about getting to the top of the leader-board. It shows you can program very well with small challenges, but that’s about it. What if your a terrible person, or can’t work with a team what so ever? No one knows, and that’s probably more important than actual coding skill most of the time.
Id consider most of those at the top of the leader-boards being the kind of person that wants to be the best at what they do (namely the coding challenges) not the kind of person that is doing it to get recognized for a job. (they might do it to get recognized tho)
Anyone probably would have a better chance at getting an interview and a job by spending all that time doing resumes, updating their portfolio and sending excellent resumes literally everywhere. Obviously you need some skills to put on your resume and portfolio, and being good at these coding competition websites is great to put on those, but that’s about it. There’s a lot more to getting a job, or even an interview than just coding skills.