It's irrelevant if a majority believe it or not. The 'majority' as you describe it aren't evenly distributed, so there are plenty of rural areas where decisions would be made by parents to have it excluded.
There's been multiple instances in the last 20 years by school boards to insert intelligent deisgn or creationism into schools in an attempt to minimize evolution.
https://www.pewresearch.org/religion/2009/02/04/fighting-over-darwin-state-by-state/