In my personal opinion, the practice of calling non-mormons (including Jews)"gentiles" may have started because the early LDS made much of their church being different, or "peculiar". They did NOT want to be seen as just another Christian church, and the "gentile" label illustrated the difference. In my time as a mormon, there was quite a distinction made, and much pride taken it it.
Gentile
Latter-day Saints Church usage
Main article Mormonism and Judaism.
In the terminology of The Church of Jesus Christ of Latter-day Saints ("LDS Church"; see also Mormon) the word Gentile takes on different meanings in different contexts, which may confuse some and alienate others. Members of the LDS church regard themselves as regathered Israelites, and so sometimes use the word "Gentile" to refer to non-members. In such usage Jews may be colloquially referred to as "Gentiles" because they are not members of the LDS Church. However, the traditional meaning is also to be found in the introduction to the Book of Mormon, in the statement that it is written to both "Jew" (literal descendants of the House of Israel) and "Gentile" (those not descended from the House of Israel or those of the tribe of Ephraim scattered among the "Gentiles" throughout the earth).
In order to avoid confrontation and pejorative connotations, Latter-day Saints in the 21st century avoid using the term "Gentile" in everyday matters, preferring "non-member". "Gentile" is usually reserved for discussions of scriptural passages.
I will never understand your double standard those who were not part of Jewish faith would have been considered gentiles,
When the Lord restored his Church again on earth anyone not being a part would be considered gentiles.
Just like many of you want to feel because the LDS doctrine does not meet you Tradition of men version in your mind the LDS are not Christians.