Happened because of the "Velvet Revolution" (https://en.wikipedia.org/wiki/Velvet_Revolution) which was yet again the people pushing the government to do something. I think when parent said "No country likes itself to be split apart" they refer to the current people in power (the government), not the people actually living in the nation. Otherwise all successful independence efforts can be considered "The country wanted to be split".
As the industrial heartland of Spain, a lot of non-Catalans live in Catalunya. They don't want to suddenly find themselves in a foreign country. That's not "the people in power" - that's ordinary people.
There's quite a lot of nationalism in Spanish politics; when Franco died, there was no proper national reconciliation. Catalunya suffered quite badly in the Civil War and afterwards, and there should have been something like the SA Truth and Reconciliation Commission. Instead, they restored the monarchy, which was, as you'd expect, nationalist.
