"Don't Know Why" is the debut single by British London-based trio SoundGirl from their shelved debut studio album. The single was released on 19 June 2011 as a digital download in the United Kingdom. The official remix features teen rapper Mann.
A music video to accompany the release of "Don't Know Why" was first released onto YouTube on 27 April 2011, at a total length of three minutes and forty-six seconds.
"Don't Know Why" is based on the track "Why (Does Your Love Hurt So Much)" by Natasha Thomas, which was released in 2003 by Epic Records and is in turn based on Carly Simon's 1982 single "Why". The SoundGirl and Natasha Thomas tracks both build on the success of the signature reggae/pop sound of Ace of Base.