Most of the non-malicious spam that we see in search results relates to fake search engines. The operators of these sites make money by tricking users into clicking on disguised advertising. Another way they make money is to convince users to install adware onto their computers as they will then receive a fee from the adware vendor.
For example, LoudMo is a well-known adware vendor. Their affiliate network pays $1.50 per installation.
Spammers don't hesitate to trick users into downloading such adware. They hack legitimate web sites to pollute Google search results, and then redirect users to fake video pages.