The phrase "reason for the attack" refers to the motive or purpose behind perpetrating an act of aggression or violence against someone or something. It highlights the underlying cause or justification for the attack. Full definition
There are good reasons for these attacks on traditional narrative vision. (religion-online.org)
Douthat believes that there is a full scale war being waged by secularists against the free expression of Judaism and Christianity (in particular) outside of house of worship walls, and gets into some reasons for the attack on the first liberty area mentioned in the First Amendment. (firstthings.com)
OBL very explicitly called out US bases in KSA as a reason for the attacks by AQ. (politics.stackexchange.com)