Why artists struggle to stop politicians using their songs

Guardian has an interesting article about how artists are unable to stop politicians to stop playing their songs at political rallies. It just so happens that's it's mostly conservative politicians who played songs that they weren't allowed to: Donald Trump played Pharrell Williams' 'Happy', John McCain played Abba's 'Take a Chance on Me', and so on. Neil Young, who also asked Donald Trump's campaign to refrain from playing 'Rockin’ in the Free World', eventually relented, saying: “Once the music goes out, everybody can use it for anything.”