The option to create resource pools is disabled unless VMware DRS is enabled on the cluster.
The New Resource Pool option is disabled because the hosts in a cluster are meant to be interchangeable in case of host failure. Host-level resource pools in a cluster may dramatically impact the behavior of the virtual machine if it were to be failed over to another ESX host in the cluster to which the resource pool does not belong.
Enable VMware DRS on the cluster to enable the Resource Pool option.
Note: A vSphere Enterprise or Enterprise Plus license is required to enable DRS. For more information on licenses required to access the different vSphere features, see vSphere Editions.