And the sovereignty of the government comes from the social contract. When a big part of the citizens feel that they are not represented by the government, the social contract is broken.

https://en.wikipedia.org/wiki/Social_contract

The Spaniards seem to love Rajoy, as they give him the majority in every election. Rajoy's party, "Partido Popular", is voted by less than 8% of the Catalans.

So, the question is, why the Catalans need to be governed by a political party, that not only rules against them, but that does not represent Catalan society?

There are more than 2 million people that do not accept the government of Madrid. How will Madrid rule over all this people without transforming Spain to a full-blown dictatorship again?