I don't think you have the right mental image of Spanish blinds (persianas). They are indeed built into the window frame and are fully retractable. The windows also open to the inside.
They have a similar function as awnings, because you can have them part of the way down, so they block the sun at whatever altitude it is, while allowing you to keep the window open for airflow or light. They are also less obstructive on the facade than awnings.
Random example: https://as.com/actualidad/sociedad/por-que-hay-tantas-persia...
I've lived both in Spain and the Netherlands.
In Spain you have the wooden blinds that are vertically retractable, they can fully black-out and insulate the room, but you also always have very light translucent curtains next to them, that let light in but can block visibility for privacy.
In the Netherlands you usually only have very thick curtains that are not translucent, they fulfil both purposes in one, light/temperature insulation and privacy, but they are an inferior solution for both.
My parents and grandparents from Spain are surprised and often note how many windows in the Netherlands are wide open, particularly on ground floors, you can see everything in the house from the street. In Spain we would simply use the translucent curtains that block very little light but provide privacy. And in the north of Spain it's just as grey as in the Netherlands, the light level is similar most of the year.
We also have fewer ground-floor households, they are generally unpopular, there's often shops there at street-level, and apartments are far more common than detached houses.