but never went to the mormon church, That why most christian get upset when you call yourself christianWell Ender's is clearly the best answer here: "Christianity is a category, not a specific denomination. A Baptist, by definition, is a Christian. A Christian, however, is not by definition a Baptist." The logic in your question is faulty.
Your question would have more relevance if you instead asked why Mormons want to be accepted as "Christians," yet refuse to accept the fundamentalist Latter-day Saint groups into the fold of "Mormons."
Gordon B. Hinckley to Larry King: "There is no such thing as a 'Mormon Fundamentalist.' It is a contradiction to use the two words together."