Why was the end piano instrumental of the song Layla chosen for the movie Goodfellas?

[Hawkee]

I've always wondered how the instrumental piano ending of the Derek And The Dominos song Layla got to be associated with the film Goodfellas? Because I have the song now and I like it because it's a cool song and I heard it on one of my Guitar Hero video games. Was Layla one of the favorite songs of the director of Goodfellas? Or was it chosen because you can hear the song at various times during the movie? Because when Goodfellas was released to theaters in 1990 this song would always play during the commercials advertising Goodfellas,
What's the reason for this song being in Goodfellas?,
Bestie