I don't understand 1) Why every company doesn't use Github/Gitlab to do documentation. and 2) Why Github/Gitlab don't offer a cheaper account type for employees

I don't understand 1) Why every company doesn't use Github/Gitlab to do documentation. and 2) Why Github/Gitlab don't offer a cheaper account type for employees that don't code or even write documentation to make internal docs available to everyone. It's easier to maintain documentation when it's closer to the project. You can also automate a lot of its parts for your projects. You can create template projects and use tools like cookiecutter every time you create a new repo to have the basic structure in place. That's already half of the road.