Why is fahrenheit 451 banned from most schools

It is banned from most schools because one of the books burned in Fahrenheit 451 is the Bible.

Chances are, most districts might see the book as too 'adult' and would rather not have a student get their hands on a book, especially from the school. Parents might not agree with the book, and wouldn't like their child coming across the book, and if their kid were to read it, the district/school could get in trouble for it.