Saudi league isn't a big problem exactly because of this, people still say no to them even with more money, and yes some people go there but not all, even with 20x more money you still can't convince some people, which means that only reason anyone would ever play there would be 20x more money, that is not sustainable.
The 20 million euros were probably not enough I think. It is a lot of money, but when somebody played for Real Madrid and PSG for 18 years in a row and was probably among the best paid defensive players in the world, I think that 20 million euros is not an amount where a player and a person like Ramos snap calls. He knew that the world over there is very different from what he likes to be surrounded with and also, 20 million euros is not 50 million or 100 million. Since Ramos is quite a big name in the business and has been for a long time, I was surprised when I read this "modest" offer when compared to the offers that many of the other players who chose to go to the Saudi Professional League were offered. Not that it is not much, but it seems to be less than he himself might have expected.