A brief explanation why…
Rickrolling first began in May 2007 when a link was posted on 4chan's /v/ board purportedly leading to the first Grand Theft Auto IV trailer, which had recently been released but was unavailable because of heavy traffic.
Naturally, instead of being brought to a preview of RockStar's latest open world adventure, those who clicked were met by Rick Astley's music video for the 1987 song "Never Gonna Give You Up." By May of 2008 the prank had become a web-wide phenomenon.
After reaching 61 million views, the original "RickRoll'D" video was removed from YouTube in 2012 due to a copyright claim, though was soon reinstated before being taken down again in 2014 after hitting nearly 71 million views. The official music video has amassed more than 300 million views as of 2017.