So, renting is not silly unless you have a particular case, as you have. And let's not call it renting; it's not even that. It's a subscription to access hundreds of millions of tracks on demand. As noted by
@richpjr above, for many, me included, it's all about discovery and finding new artists and tracks you would never have heard otherwise.
Spotify gets that right, and Apple or others can't touch it. Once Spotify gets to know you, it will introduce you to many new artists based on your listening; it's virtually perfect, and much of my listening over the past two years is thanks to Spotify understanding my likes; not just that, but recommending material I like. You're paying for more than just music with Spotify. That's why it's so popular.