It’s right there in the second map. It is something quite recent; most probably due to the lower price of beer and less variance of quality.

FTA: ”The alcohol belts refer to the traditional beverages of countries rather than what is most commonly drunk by the populace today”.

Also, the second map, labeled ”Map of Europe with individual countries grouped by preferred type of alcoholic beverage, based on recorded alcohol per capita (age 15+) consumption (in litres of pure alcohol) in 2010” has Spain labeled “beer”.

Is it because one can have a cold beer as a hydration and cooling vehicle, while wine cannot fill that role?

There is a tradition in Spain of cooling wine beverages in the warm months of the year: sangria where wine is mixed with fruit juice, and more recently calimocho where it is mixed with Coca-Cola.

You drink green (as opposed to mature) white (grape color) wine cold, specially in the summer.

Oloroso muy seco para me. Does that count as wine or spirit?

Not really, wine is only dominant now in the Castilla region as internal production quality improved thoughout all of Spain.

Wine usually is more drunk with food, not really as a standalone drink in Spain.

Google "Foreign population residing in Spain", you might find it enlightening.