Which player was born in Saudi Arabia and is famous and earns a lot of money like foreign players? The answer is simple: there isn't. So these native Saudi Arabian players are just watching the foreigners come to their country and take all the glory and are taking a lot of money and in 2 or 3 years they will leave for their countries and the native Saudi players will continue to play badly. When Ronaldo retires, this league will lose attention and many famous old players will not want to go and play in this league and the Arabs will not be offering these high amounts of money anymore because this is unsustainable in the long run.
Things are not going to change overnight and you need to have some patience. At the moment, Saudi authorities have two options in front of them. Saudi Arabia is currently ranked 59th as per FIFA, and they don't have any world class players in their team. So either they can have a sub-standard league with mostly Saudi players, or they can pay huge amounts to foreign players who will enhance the quality of the league by mixing with the local players. Saudis chose the second option. And in the long-term this will increase the quality of the local players.