Do you know the tale The boy who cried wolf? Where the sheperd boy cries for help when he doesn’t need it and when he finally does, people don’t believe him and he gets eaten?
Well, that’s Harry in HPB. Why? He has accused Draco of everything evil since 1st year, but it was never Draco. Now, that it is him, nobody believes Harry because it seems like a weird obsession at this point.
Now let’s take a look at Hermione: she doesn’t do that. Harry and Ron don’t have a reason to not beleive her - to the contrary. She is always right.
So tell me again, dear Goose, is it really the same situation?