Can someone explain to me the real reasons why we're playing the Spanish cup in Saudi?

Everyone says "money" but how exactly did the Saudis influence the entire corporation behind the league to hold games in Saudi? I want the two-legs of Madrid vs Barca in the Santiago Bernabeu and Camp Nou, not some middle-of-the-desert Saudi stadium.

Where exactly did the Saudis invest funds to make this change? How are all teams on board with this? To what extent did they bribe the Spaniards?