Because it would take work and time to put such a system in place, and they are overwhelmed right now. Plus, it would certainly cost money which is probably not

Because it would take work and time to put such a system in place, and they are overwhelmed right now. Plus, it would certainly cost money which is probably not in budgets that have been cut to the bone. There's also a cost/benefit analysis. Having gone through a few hundred such applications, they have probably come to the conclusion that the likelihood of finding a gem is too low to be worth the effort. If you are employed, you are likely only sending out resumes if it's a very good fit; therefore, from the hiring HR guy's point of view, there's a lot of value in that self-selection.