It also massively increases the effort required to GM, makes the actions stilted, and obscures a lot of the information that characters would be able to build conclusions out of (because there's not going to be a full description in the thing), whilst leaving us with only the meta-gamey "Well, these people aren't fighting" and "I recognise the writing style" bits. 

And welding together people's posts is either going to be clunky stitching or intrusive rewriting, which I can't really get behind. I write my posts as I want them to appear, after all.