No one likes to be wrong, so that's certainly part of it. I also think that she may genuinely believe that they were/are together. Some people will take their denial at face value and move on. Some people will continue to wonder, and some will just flat out not believe them. People, like the TBC blogger will continue to fight their side no matter what - that's human nature. Some people believe that TH is gay, and even though he's said he isn't, and others have as well, they still refuse to think otherwise.