I'm a fan of the Lord of the Rings movies and consider them to be masterpieces of film making. Every time you watch one you notice little details that escaped your attention on previous viewings. Watching all the "making of" documentaries really drives the point home that every aspect of production was handled with extreme attention to detail - including many details that most moviegoers will never notice.
Factories were set up for manufacturing swords and armor as well as hand-made cups and plates. Even minor characters were exquisitely made-up and costumed. And these are just the things you notice after repeated viewings. There are undoubtedly many more little efforts that you'll never see, like waiting for an airplane's contrail to dissipate before resuming filming to avoid any anachronisms, or clever lighting and microphone placement, or the extensive post-production sound processing. If you think about the total audio experience, it's an amazingly good and amazingly complex mix. Every sound effect sits just right in the mix, every line of dialog is clear and clean, horses' hooves have just the right amount of low-frequency clump mixed in to give them weight and power.
Getting a quality mix requires similar attention to detail. Cleaning up barely-audible punch-in clicks, automating out noise and resonances, making sure reverb tails don't collide with the next snare hit, panning background vocals to clear the center for the lead, nudging drums to put them in phase. You do these types of things
without regard as to whether or not they'll be audible in the final product, or whether anyone will notice them. It's the cumulative effect of many little details that results in a quality mix.
Sure, at the end of the process the listener may hear a severely degraded version streaming at 128kb/s, or squashed on the radio, or through tinny little plastic earbuds, or competing with road noise in a car, or badly mono-fied by widely spaced ceiling speakers at the grocery store. But even if one in a thousand listeners has the equipment and the attention span to hear it the way you meant it to sound, then it's worth it.