Why can I only read partial essays on certain sites devoted to helping students cheat on homework?

Many sites claim to offer "free" essays for students who
are trying to cheat their way through school by downloading work rather than writing it
themselves. These sites will sometimes put full essays up for view -- which can easily
be detected by plagiarism software -- but more often put up partial essays so that the
student must pay for the privilege of submitting someone else's work for a course. These
teasers are intended to lure potential buyers to the site by simultaneously advertising
wares and making them unusable in the advertised form. Since posting genuinely free
essays limits revenue to advertising, most sites are more interested in selling you
already written essays or enticing you to pay even larger sums of money for custom
written essays. The problem with using such sites is not only limited to the dangers of
(1) downloading malware and (2) getting caught, but ebven more important, even if you
have no moral qualms about cheating, is (3) that you do not learn anything by doing this
and do not build a foundation of skills usable in future academic endeavours or a
career.