Because not everyone in the government actually likes this relationship with the US, nor did most of the government support the attack, or Al-Qaeda. Saudi Arabia, even its government, isn’t a single person, nor is it some sort of hive mind. It is thousands of people, that fight for their own personal interests, and break down into factions of different ideas over different things.
Then why would they sponsor a terrorist attack against the US?
Because not everyone in the government actually likes this relationship with the US, nor did most of the government support the attack, or Al-Qaeda. Saudi Arabia, even its government, isn’t a single person, nor is it some sort of hive mind. It is thousands of people, that fight for their own personal interests, and break down into factions of different ideas over different things.