George As a cynic I'd say, it's the competition of so many different sects and cults, see I can be even holier than you.
Some might say we're the last bastion of the true church! lol
Also, though we have many denominations, they have mostly coalesced into a few general categories.
Liberal Yankees, city slickers, and coastal elites. Evangelical Lutheran Church of America, American Baptist, Disciples of Christ, United Church of Christ, Congregationalist, Unitarian, etc.
Conservative southerners and plain old country folks. Southern Baptist, Lutheran Church Missouri Synod, Foursquare, Evangelical Free, Church of Christ, most non-denominational churches and megachurches, etc.
Churches with both liberals and conservatives. Most of these are having big internal fights right now. Episcopal (American Anglican), Methodist, Presbyterian, Catholic.
Churches with additional doctrines or extra strict interpretations. Seventh Day Adventist, Pentecostal, Jehovah's Witness, LDS/Mormon.
I know it sounds messy, but somehow everyone who wants a church can find the right one for themselves, and sometimes we even work together for the common good.
I know of interfaith organizations where liberals and conservatives work side by side to feed the homeless. Somehow they never get as much news coverage as the maniacs yelling at each other.