There's nothing sudden at all. They effectively lost their independence 300 years ago but the drive for independence has always been there (along, famously, with a few other parts of modern Spain). They have their own language, their own culture.

Their desire for independence has been around for hundreds of years.

But even if that wasn't the case: what's wrong with that? Why would a few million people that want to form a sovereign state have to be held hostage by the others just because they're wealthier?