"Google's Borg system is a cluster manager that runs hundreds of thousands of jobs, from many thousands of different applications, across a number of clusters each with up to tens of thousands of machines. It achieves high utilization by combining admission control, efficient task-packing, over-commitment, and machine sharing with process-level performance isolation" [0].

All of their processes run together on the same machines so you wouldn't want to risk one compromised process access data on possibly any other process.

[0]: https://ai.google/research/pubs/pub43438