Decades of financial support for US covert and overt military operations (including Operation Desert Storm, for which the Saudis footed over half the bill) are why administrations on both sides to the aisle have referred to the Saudi royals as allies. They are arguably stronger allies than most NATO countries, which are military dependents rather than useful allies. Our problem with Saudi Arabia is the same as our problem with the Muslim world - the Muslim man on the street hates our guts and those of their leaders who are our allies are villified by internal rivals as American lapdogs.
As a price for their contributions we are allowing them to spread their radical form of Wahabism. As they said they are in it for the long run and long run they are commited to jihad.
The Saudi government is the most repressive on earth except for north Korea. They are literally worse than iran.
When they pay for things, they aren’t being an loyal ally. They are hiring us.