Because when you run 10 services most of whom require at least one supporting service and for each service you need to specify at least 5 different options (volumes, resource limits, health check, depends on, mac address, IP address, etc); with just `docker run` you will have a mess. It's much simpler to have a docker-compose file per service with all of its dependent services.

The docker compose to plain docker run is the same as C/C++ to Assembly.