Apprising Ministries points you to a recent headline story from Christian Post which enlightens us that:

The seemingly always smiling, positive-thinking pastor to America’s largest congregation welcomes everyone to his church, including office holders and politicians—as long as they agree to leave politics outside the church doors…

“Part of it is how I was raised,” Osteen explained in a Newsweek interview this week. “My father…kept it out of the pulpit.”
(Online source)

Well, as far as I can see Joel Osteen wants to keep doctrine out of the pulpit as well because he recently said that practicing Mormons in the non-Christian cult of the Church of Jesus Christ of Latter-day Saints are Christians just like he is.

See also:

JOEL OSTEEN BLESSES THE MORMON CHURCH

MORMON CHURCH: DEITY OF CHRIST