Why is it traditionally thought that book of daniel's author is Daniel?

I understand that most scholars think that book of Daniel is a forgery and definitely not written in the 6th century BC and not written by Daniel. What strikes me is why Christians traditionally think that the book was written by Daniel ? In the book itself, first 1-6 chapters, it's written in 3rd person and not 1st which definitely don't mean at all that book was written by Daniel. For sure, 7-12 sometimes talk about in 1st person but what solid argument does this give that book was written by Daniel ? Would you be able to shed lights about why Christians think that it was written by Daniel ? what's their reasoning ?