Because you've already initiated a dialogue with and shown interest in those candidates, so they have at least some assurance that they're not just wasting their time.
How is that? All of these things are still problems once the company has said "hey, we received your resume, and now we want you to do something more":
> They could have just found someone and not yet taken the ad down.
> They could be about to receive an application from someone even better than you.
> They (or their system) might have some inherent bias against you
> When you're applying for a job it's just not feasible to go around doing HARD programming questions every time, because for so many reasons out of your control the company might just ignore you.
> you have no idea if the company is going to be interested at all
Most of those responses are going to candidates the company would never even consider hiring, because the initial filter is so worthless.
