How do you figure? Roads, water, electricity, rail lines, they all cost money, labour, and focus that could have been sent elsewhere. When the private sector wants to develop an industrial zone the government has to lay down a lot of infrastructure to enable that development and it costs billions. Those same billions could be invested elsewhere in other industrial areas but generally the private sector picks the spot for a good reason (access to skilled resources, transportation networks, etc). Thing is due to how development works you inevitably get a snowball effect where wealth congregates into specific areas. Its just he way economies develop. If each region that got lucky with that type of development decided to go independent it would lead to thousands of rich micro-states and massive regions of impoverished areas and it would not be fair. It would balloon inequality in the world. The poorer regions provide farm lands, water, etc for those industrial parts. They also often contribute the labour. Think of Mpumalanga, they carry a massive health cost due to poor air quality from the power stations that power most of SA. Yet MP is a fairly poor province. Is it fair to leave them high and dry when they have contributed as best they could but for whatever historical reasons the industrial centre of SA was developed in Gauteng and not there?
Catalan is similar. Geographically it is in the north east of Spain, so closer to the rest of Europe. Hence goods manufactured there are cheaper to export to say France or Germany than goods produced in central or southern Spain due to distance. Hence the private public partnership developed the industry in their region at the expense of development in other parts of Spain. Now they want to up and leave??? I don't think that is fair.