We haven't been writing long (in evolutionary terms) so I wonder why that is?
Thinking aloud, whether in the mind, on paper or even vocally, helps us to identify some of these points, and thus quantify a meaning from it. There's only so many points that we can mentally hold though - we're not good multi-taskers after all! So the better we can think aloud, the better we can consciously grab thoughts and identify the real gaps - which we can fill in by searching/ creating more points in our mind, or go external.
Hmm, just thinking aloud though ;)
lol just saying