Sending out the initial spams is very automated (and so cheap), but if you respond, they probably have a human handling than (maybe with templates, but still un

Sending out the initial spams is very automated (and so cheap), but if you respond, they probably have a human handling than (maybe with templates, but still under human control), which isn't nearly as cheap, so they want to avoid wasting time on insufficiently-gullible responders.