Parmandur
Book-Friend, he/him
I can't speak for anyone else, but that is exactly how I use the setting and adventure books. I use my own setting and I don't use published adventures. I just buy them to mine for interesting bits and bobs.
But I understand wanting it all in one book.
I use them to mine material, too. I appreciate the thematic organization. Want to get some Underdark material? Pick up OotA. Want some arctic material? Pick up Icewind Dale.