Although Google’s newfound enthusiasm for video has created more competition for fewer traditional search results, it has enabled sites with video assets—even sites that would otherwise score poorly in the Google index—to successfully achieve first-page rankings.

Search engines look at a variety of signals for ranking purposes, as well as spam detection purposes. This includes a site review to determine if it's over optimized, and can result in the rankings for a site being dropped to a lower position than they may otherwise occupy.