I did resume screening for about fifteen years for different small companies, it’s first because if I phone screened everyone who sent an letter or email expressing interest there would be no time for anything else and I would be wasting a lot of candidate time when I could look a resume and know if someone was ballpark decent and just let both of us off the hook early with rejection (a lot of people swing for the fences with applying for jobs) if this was easily ascertainable from the resume. I am assuming candidates are making the best argument for themselves in their resume.