Since no one else has brought this up, I think one of the big drivers behind this project is actually another eclipse project (che): https://www.eclipse.org/che/technology/

Che is a cloud ide that is supposed to be easily deployed into a k8s cluster. Che supports authentication and spinning up pods for projects, and other management features. Theia may have been developed to work nicely with Che directly (I am not a developer of either so this is only speculation).