And the relationship of Scouting to "mainline" churches is curious because you'd think Scouting's values would align more with evangelical churches -- but I know many S. Baptist churches don't sponsor Scout troops because of the fear that Scouting would take members from the Royal Ambassadors.
I think the key is in your use of the word "supposedly." I don't trust polls.
The evangelical churches I know are plenty involved in community outreach. :-)