“After running several workloads inside, you end up with an idling VM that consumes 32 GB of RAM on the host, even though it doesn’t need any of it.”
Firecracker never hands RAM back to the host, and deleted files inside the VM never free disk on the host. That is fine for AWS Lambda, which kills the VM after one function call. It is a disaster for a dev environment that runs for weeks. “Minimalist” means minimal for Amazon’s use case.