It is absolutely in Google's best interests to externalize security for its customers as a differentiator of Google Cloud. The parent article itself links to the white paper that outlines how this is done for Google Cloud.
I understand how one may consider this a "closed ecosystem" from one perspective. However, from a customer point of view any startup or mom-and-pop can leverage these very complex and expensive world-class security developments, whereas in the past this access has been reserved to the very select few that could afford it. When the barrier to entry is lowered and access is commoditized, customer wins.
(work at Google cloud)