Shitty recruiters do this shit because at the end of the day, it still works. Or works well enough for them to make a decent salary. Really shitty recruiters quit after a year or two because their base salary is very low (or even zero) and they don't get their commissions if they don't get placements. Ignore them and they will literally die off.
All the Engineers, Designers, Developers who complain about this practice should just put these recruiters on blast. I freaking LOVE what DHH is doing with those stupid recruiter emails. Why don't all of you do that? Those shitty recruiters will be on notice, their Agencies will be embarrassed by the bad PR or Google Search results and no startup will use their services.
At the end of the day, a good recruiter (full disclosure: that's my day job) will still be in demand because they do more than push resumes.
Cheers, Hong