There have been posts recently asking questions about Automattic’s involvement in Gutenberg compared to other contributors and companies. There is no secret conspiracy here — as project lead I was able to enlist the help of dozens of my colleagues to contribute to this project, and I knew that a project of this size would require it. Automattic aims to have 5% of its people dedicated to WordPress community projects, which at its current size would be about 42 people full-time. The company is a bit behind that now (~35 full-time), and the company is growing a lot next year, so look for 10-15 additional people working on core and community projects.
In the end, Gutenberg is similar to many other open source projects — Automattic will benefit from it, but so will everyone else in the WordPress community (and even the Drupal community). It’s available for everyone under the GPL. If the goal was purely to benefit Automattic it would have been faster, easier, and created an advantage for Automattic to have Gutenberg just on WP.com. That wasn’t, and isn’t, the point.