It's because 'Spain' is a noun, while 'there' is an adverb. Prepositions of place ( in, on, at) or prepositions of movement (to, into) combine with nouns (such as Spain, or home, or school, or cinema) to tell us where something or someone is, or where they are going. The words 'here' and 'there' are adverbs, so you don't need a preposition of place or movement. If you like, you could think that they include the preposition. Other examples of adverbs which work in a similar way are 'abroad' or 'upstairs'. These words also tell us where someone or something is, or where they are going, and they do so without the need of a preposition. I hope that helps.

Why are we here? I would say it's just because

Yes. I like your answer. I appreciate your time and consideration.

Grammar describes how words are understood to be used in a language so that people can know the meaning. By analysis of the sentences, we know that the speaker means a future action, or a past action and the rest of the meaning. It describes what happens, for common understanding. Lanuage evolves. People are not logical. The language is not substantially controlled byt an overseer who imposes rules. . I think you will find in many languages, especially English, that there are rules and exceptions. So the rules made to make it seem as if it has some underlying logic, don;t work in all cases. So you have to make extra rules with conditions. . Often the constructions used in a language seem consistent as this aids people to understand and extrapolate to new constructions. For example we get things such as That just does not sound like "English". . So, it may be that someone can give you a rule that sounds consistent, but grammar describes language, something which does not required the underlying logic that you crave. . I undrestand: you need a rule that covers most cases, so you can know how to create sentences "correctly". . Go to has so many strange things. . Rule: Go to Spain Go to the shop Go to Bloomingdales. Go there Go shopping Go to meet them. Go quickly. Go quietly. . Perhaps you can have a rule to describe this as no "to" before Proper nouns and here,there (adverbs [of place]) . Maybe someone else can give you a formally accepted rule that covers most cases. . Sorry for the bad news. There are rules that are, atleast useful. Search for them.