The Church of Jesus Christ of Latter-Day Saints was birthed back in the 1800s by an alleged vision in which two celestial personages appeared to Joseph Smith and claimed that all existing churches were wrong, that all their creeds were an abomination and that all their professors were corrupt. According to this vision Smith was chosen to restore - not reform - a church that, in his view, had disappeared from the face of the earth.
The Mormon doctrines that evolved from this vision compromise, confuse, they contradict the nature of God, the authority of Scripture and the way of salvation. In fact, while Christians believe that they're going to stand before God dressed in the spotless robes of Christ's righteousness, Mormons contend that they're going to appear before heavenly Father dressed in fig leaf aprons holding good works in their hands. According to the Latter-Day Saints just about everybody qualifies for heaven. The world's vilest people will make it into what's called the telestial heaven; lukewarm Mormons, religious people, they're typically going to enter a terrestrial heaven, and temple Mormons are going to make it to a celestial heaven. Only those who are sealed in secret temple rituals will make it to the third level of the celestial kingdom and then become gods of their own planets.
These and many other doctrinal perversions are why we exclude Mormonism from rightly being called Christian.