Because "the additions to Daniel," three chapters, were not found in the Hebrew or Aramaic text, and were not part of the Jewish Tanakh.
"The additions to Daniel" are contained within "Protestant" Bibles as part of the Apocrypha or Deuterocanonical books, which are bound separately in the back. They're regarded as edifying but not divinely inspired.
Some more recent "Protestant" Bibles do not contain the Apocrypha, however no one "deleted" anything.
"Bel and the Dragon" is regarded as Apocryphal by "Protestants" too, would you like to discuss that one?
Thanks.