ESXi can't add new VM to port group once VMKernel NIC attached to group

I'm using ESXi standard (the free version) on a new server. When creating a new VM via the embedded host client UI (the new web client that isn't vSphere web) I cannot add a new VM to a port group once the port group has a VMKernel NIC attached to it.

Does anybody know why this is? If I create a new port group, where the only difference is that it isn't attached to a VMKernel NIC, I can add the VM to that port group.

I'm new to ESXi, so sorry if I've missed something obvious, but I can't see any obvious options and Google doesn't turn anything up.

Just create a second port group for your VMs on the vSwitch. You can have multiple port groups egressing out on the same uplink & VLAN.