Very interesting "coincidences" here.

Spain treats their Catalan subjects pretty badly, often using riot police to violently suppress unrest, but they are a region of Spain with very high economic productivity and their own language and cultural heritage. Catalonia is a net exporter to the rest of Spain, contributing 20% of national GDP (http://catalonia.com/catalonia-barcelona/diverse-open-dynamic/competitive-economy.jsp) with only around 16% of the population (https://worldpopulationreview.com/regions/catalonia-population). The main reason for Spain to decline to grant Catalonia independence is therefore economic: Catalonia contributes more per-capita to the Spanish economy than the rest of the Spanish themselves, including the capital city of Madrid.

"Catalonia would need Spain's permission if it wishes to eventually re-enter the EU following secession" (https://en.wikipedia.org/wiki/Catalan_independence_movement#Long-term_prospects) - OR - to look at it another way, Catalan independence would be yet another death blow to the EU.

Independisme Català!