Docker has become a de facto standard for executing programs in a portable sandbox (aka "container"). There were increasing demands for making it a "proper" standard, so last year we donated a spec and reference implementation for a universal intermediary format - a "PDF of containers" if you will, and partnered with the Linux Foundation to manage it. The majority of the industry followed.
Now that the Docker container engine supports this intermediary format, and other providers will soon follow suit, it reduces the risk of depending on one provider. If you want to switch away from Docker, you can run your containers elsewhere.
Now everyone can focus on building better tools, instead of trying to make "their" format win. The result is better tools.