Google Cloud's PubSub product offers a few advantages that would likely be cost reducers and/or more efficient for adopters deploying to Google Cloud as their infrastructure deployments.
On-demand managed service, allowing reclaiming k8s cluster resources from the strimzi-deployed kafka cluster
On-demand/FaaS based so topic management is dynamic
Google Cloud team maintains elixir api client libraries for PubSub on Hex.
Elixir core team already provides broadway interface to Cloud PubSub
Google Cloud's PubSub product offers a few advantages that would likely be cost reducers and/or more efficient for adopters deploying to Google Cloud as their infrastructure deployments.