That's because real physically imposed signaling limitations do not apply in a virtualized environment between two VMs on the same host and port group. OSes don't artificially limit traffic to match the agreed on line speed unless it is physically required.
You'll also get more than 1Gbps with a pure 1GbE emulated vNIC like the e1000, and more than 10Gbps with vmxnet3 in Linux for example, for which iperf is optimized (I got 25Gbps between 2 Linux VMs with vmxnet3 on the same host/network).
On a side note, I don't see the point you're trying to make by applying this limitation in the device properties inside the guest.
Ok. Is there any way to limit bandwidth on a VMXNET3?