There are tons of objective reasons to promote local products, we have incredible soil and weather, we have a historical tradition of shepherding and sea faring. But none of that is promoted, its the "its from here" with vague connotations.
It is a large corporation that has had a huge trouble expanding outside the local area of influence. Eroski has been a huge supermarket in the basque country for decades and has never hold more than a minimun influence in spain (despite other supermaket chains like Mercadona appearing much later and now dominating the country). Fagor grew steadily to 5,600 employees and then went bankrupt leaving all but 700 unemployed when a company from elsewhere bought the remains. The university has 4 thousand students and most are basque.
They are massive but they are massive because they have a huge influence on a very rich part of spain