Luther didn't (strictly) "drop 7 books from the Bible." He did use the short (Jewish) list for his Old Testament rather than the longer list that Western Christians had used for over a thousand years. But the longer list used by Catholics was not made absolutely official until the Council of Trent (1560's), that is, after Luther; so in that sense, Luther didn't "drop" them.
The 7 funky books that the Catholics use that Protestants don't either were not written in Hebrew, or in some cases, were written in Hebrew but the original had been lost. Jews required a Hebrew original,and Luther used the Hebrew list.
And yes, Luther did not like some of the stuff in the 7 funky books, and that undoubtedly encouraged him not to use them.