Because Delta doesn't have the resources to hand score their 10,000+ airline applications. At this point in the hiring wave, nearly everybody who has received an invitation for an interview has either gone to a job fair, or had a current or retired Delta Air Lines pilot submit a recommendation directly to HR.
To answer your question, I don't know that the application in question hasn't been scored yet. I'm just going off of the fact that the overwhelming majority of people on these forums who have received an invitation have done one of these two things.