For a number of reasons, I believe this.
* You don't get the rush of external validation
* You are heads down trying to make things better at the company and blog posts don't help (enough)
* It's hard enough to share bad newest with employees and investors, who wants to share it with the world
* You may fear scaring off customers ("I was going to mattermark but then they seemed like they were going out of business so I used competing project")
Say what you want about the company, product, and executive leadership, but for a time Mattermark was a fairly influential organization in the Valley and elsewhere.
Mattermark can probably serve as a case study of how good written content can really bolster a company's credibility and positioning in a market.