Some points:
* As far as graduating seniors, when you post a job offer, you get maybe 10% of the resumes from people with either a CS/CE major or minor. That's not to say they can't code (in my experience a resume from a non-CS major with good experience is a much better bet than a resume from a CS major with little or poor experience). But we literally get people whose experience totals up to "took a 'How to write HTML' class once freshman year as an elective" applying to jobs involving low-level C
* Actual on-site interviews are very expensive; unless you are really hurting for people, you need a cheaper (and potentially less precise) way of weeding things out.
* With the exception of graduating seniors, there really are relatively few good candidates actively seeking work; most of the good ones have jobs (and you can hire them, but that usually isn't counted in the X% of resumes get offers, which usually refers to responses to a job posting; hiring people away from their current jobs usually starts in a different manner).
* On the other hand huge numbers of people who are desperate for work send in resumes. The less harmful of these are the ones who obviously are unqualified and clearly just spammed every job offer listed regardless of the requirements. Since we aren't talking about graduating seniors (see above) the majority of the not-obviously-unqualified often even have relevant work experience, but that's just because it takes time for people to fire you.
I am talking about people with 2-5 years of experience working in language X who are barely able to (or sometimes even completely unable to) write FizzBuzz in language X.
Another example was someone with over 5 years of OS kernel development, who in the interview was unable to describe what exactly they did in those 5 years and they didn't seem to know a much about any of the various OS topics we tried asking them about: scheduling, interrupts, DMA, filesystems, memory paging, IPC.
These people are particularly harmful, since there are very few tells at all on their resumes (and no reliable ones), you would have to interview all of them, which gets expensive. The majority can't get past a phone-interview, but when you are talking about
This leads to a lot of companies not even bothering to interview people (again ignoring those graduating from school) without referrals from current employees, or some other way of weeding out the massive numbers of "good resume, but bad candidate" submission that also will, as a side effect, weed out some of the "good resume, good candidate". It also means that if you are looking for work, and can't find it, then either you are unqualified, or need to get referrals from friends who have jobs at companies that are hiring.