In the case of developers, truly elite talent is not compensated anywhere near 10x (or 100x) the standard-issue rate (unless they become founders). Thus, there is a massive incentive to cast a wide net, and hope to land a big fish for whom circumstances have misaligned.
For prospective employees, the best jobs are typically those one obtains through a network rather than a recruiter anyway - leading to a reluctance to engage, thus requiring a wider net.
Bottom-line, a few elite recruiters can and do behave differently. A few elite developers can and do earn more, and for the rest of us mere mortals, this paradigm is probably the equilibrium. Curious if automating responses to automated emails would lead to ever larger/wider outreach?