In an ordinary context, where a person is speaking about a decision which has already been made, but is still valid, the present perfect is the right one. The decision happened before now, so past simple is not appropriate. If the decision is ongoing, that is, you haven't finished deciding yet, you would use present continuous, not present simple.
In those contexts, if I read or heard the past simple or present simple, I would think, "oh, they must have meant to use the past perfect".
In the context of telling a story, past simple or present simple are used to say that the decision happened at the point in time being described in the story. This is more common in literary contexts.
It's possible you found many examples of the storytelling contexts in written works because we often use written works to tell stories.
You seem to ask if past simple is a simpler form of present perfect, if I understand you correctly. If so: no, while in some contexts they might mean very similar things, in general they have different meanings and uses, you can't simply replace one with the other.