Running OpenStack for this is a massive project cost compared to spinning up a few local services, and the operational mess is on a different planet from "I need to fake a handful of API calls on my laptop". Self-hosting still means updates, drivers, and k8s/OpenStack glue code. Nobody sane are doing that for local dev, use Minikube or Podman if you want DIY and still like weekends.

I'm saying not that OpenStack can replace LocalStack, but instead that LocalStack, by building a project on top of proprietary APIs, set themselves up to fail.