This is not really a question. More of an observation. I really just memorize it by hearing it multiple times.
Estoy aquí por negocios. I’m here on business.
Estoy aquí para bucear. I'm here to scuba dive-
The first sentence with word "on" is translated as "por". I would have thought that "on" is "en" in Spanish and "por" is "for"
The second sentence with the word "to" is translated as "para". I would have thought "to" is "a" in Spanish and "para" is "for" in English.
More on por and para

Ava Dawn
December 30, 2014

Dan-H24
December 30, 2014
Aurora, I think this is one of the challenging aspects of learning Spanish. My instinct is to try to translate literally: "I'm here on business" should simply translate as you suggested. But we know it is not that simple.
Maybe it is the interaction of prepositions like por, para, en, a with the words that describes what they are for, in, or to. Or maybe it is the context of the entire sentence. Or maybe some things just are what they are, and as you say, we need to memorize which to use when.
This article provides some insight into the issue:
http://spanish.about.com/od/prepositions/a/prepositions.htm
Dan