A writer’s main goal is clear communication. Even if you have the most excellent point in the world, if you can’t communicate it clearly, no one will understand it.
Writers will intentionally leave some things bare, so that it can be clearly understood the first time, and strikes up a healthy desire to do further research. Belaboring a point doesn’t provoke deep interest with the average uninterested target.
Promotional writing is a good example of this. An advertisement is not supposed to be a long explanation of every facet and value of a product. The potential buyer doesn’t want to know everything about the product in the ‘information collection’ phase. One of the most enticing pieces of product advertisement for the consumer is the option to do his or her own research. An advertisement is simply the enticement to learn more, the invitation to be curious.
If you bore your audience with details, their curiosity has nothing to latch onto. Over-explanation is the death of wonder, and the birth of boredom. And a bored audience doesn’t buy your project (or support your kickstarter, or subscribe to your magazine), they look for something else that better entertains them (or interests them, or validates them, or just isn’t boring).
It isn’t always easy to write clearly and provide adequate information while still provoking interest and curiosity, but if writing weren’t a challenge, there would be no satisfaction in the victory of success.