They didn't used to. Their religion doesn't resemble the original church (the one Jesus built) very much.

The original church didn't
have temples
have 'tokens'
have 'sealings'
have a savior related to satan as a half-brother
have an 'aaronic priesthood.'
have ANY Melchizedek priests OTHER THAN JESUS CHRIST HIMSELF
baptize anyone who had died
encourage folks to work towards 'exaltation' to becoming a god themselves
etc
etc
etc

So why do mormons CLAIM to be the same as the church Jesus Christ built?