Summarized neatly, in a single paragraph, by Kirk McElhearn writing for Macworld:
iTunes initially came into existence because of “a music revolution” guided by Steve Jobs, who, as we know, loved music. Over the years, as digital content matured, iTunes became the hub for all that content. That’s not a bad thing in and of itself; lots of people love to call iTunes “bloated,” but I disagree. The problem now is that those who want to use iTunes for its original purpose, music, find themselves stuck in a morass of features designed to sell, sell, sell product from the iTunes Store.
I am a longtime, traditionalist, boring iTunes user. I have an enormous collection of painstakingly-catalogued local files and not much else in my library. For my use, iTunes has become steadily worse over the years, as I’m regularly pushed to purchase more from the iTunes Store and place all my music in iCloud. Neither of those things appeals to me. Yet, I’m compelled to continue using iTunes partly because I sync my iPhone in the old-fashioned way, and partly because I’ve never found a compelling replacement for it.
There is a part of me that hopes I never find a replacement; I simply wish for a vastly-improved iTunes. I have a hunch that I’m not exactly the target demo any more, though.