As you know, Bob...dialogue is, like, when characters talk to each other
I'm reading The Samurai's Daughter, a mystery by Sujata Massey. I've always enjoyed her mysteries, but I haven't read any for a few years and so have missed the last three or four. She writes a good story, but I'd forgotten in the interim that one of the reasons I hadn't gone out of my way to search them out is because her dialogue is really reek-a-riffic:
[the main character, Rei, talking to her father at lunch]
"...Now, Dad, where were we? The ten grave precepts of Buddhism. The ones your grandfather felt were so important to live by. I thought it was interesting that he had them on display."
"Yes they were recorded on a calligraphy scroll. I think it originally came from a monastery, but it hung in the office where he worked. Unfortunately, I don't know where it is now."
"Do you recall, approximately, what it said?"
"The precepts. You know them, don't you?"
I rolled my eyes. "I know some of them, but not all. You didn't raise me Buddhist, remember?"
"But you did take an Eastern religions class at Berkeley, yes?"
"It was so long ago, Dad. Just tell me. This is an oral history project, not a go-to-the-library project. I remember the first one..."
The dialogue is all about the information and not even a little bit about the characters or their current emotional state. And the interesting thing is that it's not likely to bother a lot of readers because if you don't have a particular ear for dialogue then you won't mind that all the chracters sound alike and that they convey information to each other that they already know, as long as it doesn't actively interfere with the story. This doesn't. It does, in its clumsy way, move the story forward at least.
But because the dialogue generates no interest on its own, the story has to be good enough to carry on narrative alone--there isn't anything else there for the reader to latch onto.
Writers don't have to be good at every tool: dialogue, setting, plot, pretty words, etc. But the fewer tools you have available, the stronger each one of them has to be.