I'm convinced that McCaffrey continued Pern long after it was best to continue and her children have tried to keep it going. It moved from being a story to the bread winner and even though she wrote many other books, only Pern got the major attention.
Also most authors are not rich, even a very successful series doesn't make them rich. IT might earn them a decent income, but even then many an author who has quite a notable and popular series is still pulling a regular job, or can only rest on the books income for a while before they have to head back into regular employment.
Those that make it into richness tend to be the exceptional few and often its only when merchandising and film/tv rights appear on the table to provide a secondary income source.
I think it also shows how little advertising and attention is drawn to authors and I often feel that publishers have allowed themselves to get stuck in a position where by they lack resources and contacts for advertising all but their one or two flagship books. I think this directly builds into the inability for authors to branch out. Yes you can argue that nearly every author puts a list of published novels at the start of each book, but that rarely works it would seem.
Heck even big named authors still have many works people never hear of. Many Tolkien fans have never heard of Mr Bliss and I've yet to meet more than a handful of Pratchett fans who've even heard of him writing anything that isn't Discworld let alone read it (his latterly published collaboration book aside as that did get quite a bit of marketing)
So I think part of it is sometimes not a lack of respect but rather that authors get stuck. Even when the magic of their setting has gone or even if they just want to branch out for a little and write something else; they find that it just doesn't put the food on the table.