It's located in Spain, a country not known for its vast wealth. Plus, it's in a special administrative region in Spain, the Basque Country. They enjoy subsidies and favorable treatment from the regional government.
Basque country is, again, rich because it has an special tax treatment and could be considered a tax heaven to some extent.
I'd say its a well developed region comparable to Northern Italy. Both were badly hit by the Euro. Had they kept their own currencies, they'd be closer to Sweden or Southern Germany.
Spaniards tends to have this idea that Spain is a shithole when it’s really one of the best countries in the world.
Its looting of the gold and silver from S. America apparently didn't help.