Fajrdrako posted about why we like books. I replied.
Nothing in this reply is a definitive answer of course, but it's here to open a discussion.
When people ask me "Are you a science fiction fan?" or "Do you like mysteries?" I'm always at a bit of a loss
I always say just that - depends. Often not only of the specific author, but of specific pieces.
I don't think the defining term you're looking for is music of the words. Especially given that it isn't necessarily about the actual words, as you say. It's about the 'it'. And the 'it' can be different, not only between different people (as audience), but also between different authors or pieces for the same reader. I like Holmes differently in the stories and in Jeremy Brett's portrayal. And to a certain extent, I like (at least the first ep of) Cumberbatch's Holmes, again differently. Yes, they're different media, but that isn't the source of the difference. They have different 'its'.
For me, it wasn't Conrad (whom I found ponderous), Gibbon (whom I haven't read yet), or Coleridge. It was Milne and Byron and Dickens and Raymond Chandler.
And for me it's none of these. Although Coleridge used to be my favourite Romantic poet (not that I've looked much at poetry in the last 20 years - GOD, it's been 20 years since my BA!).
I don't know that I could name favourite authors in absolutes. Depends how one measures it, too. There's works I go back to repeatedly, but that doesn't mean I necessarily consider them my favourite. I wouldn't define Dorothy Sayers or Conan Doyle as favourite authors, although definitely favourite mystery writers. I love Good Omens and keep reareading it, but neither of the authors is my favourite. There's a possibility Monte Cristo is still (or again) my favourite book, but I could never stand any of his other novels that I tried.
Which leads us neatly back to your final question (with the required change of authors, as I haven't even read any of those mentioned below):
Why Heinlein, but not Dan Simmons? Why Stan Lee and not Mark Waid?