How much say do the people working on a team have, in who gets hired? I mean people who'll actually be working with the person day to day, not some manager.
If the answer is 'we tell recruiting agencies we're hiring for vague role X, Y and Z', then why are you surprised?
Is the work any interesting? No? Generic corporate codebase perhaps? And you're getting generic people applying? How strange :)
ps. This is not directed at you in particular. I just find it strange when people don't do an inch beyond 'we pay money', and then expect a mile beyond 'i do just enough to get paid'
Retaining staff doesn't mean that you aren't hiring at .2 headcount per annum.
Assuming that there's a basic process of CV review (by team members who would work with) followed by non technical phone interview. You will still have people who fail fizzbuzz. I'm not talking about small errors reading the problem - but the inability to even put a for loop in pseudo code onto the page.
The fact that the test is required is somewhat silly - but it's hardly limited to dull corporate roles.
See, you are assuming a basic process of a job board and anyone applying for the position.
I am saying you are so entrenched in mediocrity that you can't fathom there are much better ways.
I will say this though - they all require a fundamental shift from 'fill seats with people for minimum amount of pay, to do uninteresting work, with least amount of complaining' to actually giving a shit about people you work with, yourself, and your life :)