The "why" is in the second sentence: "Nomad is a simple and flexible orchestrator used to deploy and manage containers and non-containerized applications across on-premises and cloud environments."
If you need a workload orchestrator for heterogeneous workloads (i.e. not just Docker) and need something that is simple then Nomad is for you.
If you need a workload orchestrator for heterogeneous workloads (i.e. not just Docker) and need something that is simple then Nomad is for you.