This is basically an argument that contingency recruiters are bad. You should differentiate this in the title from in-house or contract recruiters (retained search). Contingency recruiters, as you've noticed, have no incentive to filter out junk because they can just take a throw it at the wall and see what sticks approach.

Also, there are a ton of bad recruiters, just like there are a ton of bad engineers. There are awesome recruiters out there and the sample of those who have cold called you rather than going through trusted channels is likely strongly biased towards the bad.