The short answer sounds petty and mean, but it’s true nonetheless: Luther jettisoned those “extra” Old Testament books—Tobit, Sirach, 1 and 2 Maccabees, and the like—because they were inconvenient.
So that is the short answer. Of course we all know that reformation was a rather slow process of decay. So here's the long answer:
However, the deuterocanonical literature was (and is) prominent in the liturgy and very familiar to that first generation of Protestant converts, so Luther and company couldn’t very well ignore it altogether. Consequently, those seven “apocryphal” books, along with the Greek portions of Esther and Daniel, were relegated to an appendix in early Protestant translations of the Bible.The phrase "Luther jettisoned them" by itself might be misunderstood by some five-year-old as if Luther personally went and ripped pages out of Bibles. But literate people tend to read in complete paragraphs and tend to understand phrases in context.Eventually, in the nineteenth century sometime, many Protestant Bible publishers starting dropping the appendix altogether, and the modern translations used by most evangelicals today don’t even reference the Apocrypha at all.