J.D. Souther was one of the most important songwriters in the hit catalog of the Eagles, but he was never a member of the band. In an interview in 2021, the country and rock icon weighed in on why he never joined the mega-successful group. Souther co-wrote some of the Eagles’ biggest hits, including “Best of My Love,” “New Kid in Town,” “How Long,” “Heartache Tonight” and more, but despite his major contributions, he was never an actual member of the Eagles. In an interview in October of 2011, he explained why not. Souther was in a duo with Eagles mainstay Glenn Frey called Longbranch Pennywhi…