Citation needed. gvisor seems to be under active development and just added support for the systrap platform, deprecating ptrace: https://gvisor.dev/blog/2023/04/28/systrap-release/
https://cloud.google.com/blog/products/serverless/cloud-run-...
Obviously there might be many reasons for that, but as someone who worked on a similar gvisor tech for another company, it's dead in the water. No security expert or consultant will ever sign off on a process isolation model. Despite of architecture, audits, reviews, etc. There is just too much surface area for anyone to feel comfortable signing off on hostile multi-tenants with process isolation regardless of the sandboxing tech.
Not saying that there are no bugs in hypervisors, but the surface area is so so much smaller.
Disclaimer: I work on this product but wasn't involved in this decision.