DRS Functionality with ROBO Enterprise License is not full DRS functionality.

There are some limitations you should be aware of before you initiate maintenance mode on a ROBO Enterprise cluster. On a ROBO Enterprise cluster, DRS is deactivated by default. If you have migrated from a DRS supported license to a ROBO Enterprise license, you may have VMs with affinity or anti-affinity rules present in the system. You must deactivate or delete VMs with affinity or anti-affinity rules or the ROBO Enterprise maintenance mode operation is deactivated. ROBO Enterprise maintenance mode operation is deactivated if DRS is not set to fully automated mode. DRS automation level must be set to fully automated mode in order to evacuate VMs automatically through the host maintenance workflow. If a VM overrides DRS fully automated mode, you must evacuate the VM manually.
Note: ClusterEnterMaintenanceMode is an API that takes a list of hosts in the cluster as input and returns a recommendation of hosts that the server can successfully evacuate given the existing constraints in the cluster. This API is not available with the ROBO Enterprise license.
Note: Due to dependency on ClusterEnterMaintenanceMode API, VMware vLCM cannot automatically put hosts into Maintenance Mode during full cluster remediation if there are VMs on the hosts.