what's wrong with
git clone
go build
systemctl restart my-service
Why would I want to proxy through docker?
This question refers to the benefits of containerization and not Kubernetes. But to answer your question: your command is dependent on (1) the availability of Git, (2) Go and (3) systemd on your host OS. Without containers, this list of dependencies is dynamic and can change in size for every project. With containers, the list of dependencies reduces to one dependency only for every project: Docker.
I agree it's expensive though. A docker-compose.yml on a VPS usually works fine as well. Requires some additional configuration outside the Docker ecosystem though.