Setting up the bridge is only half the battle. By default the OS isn't going to pass traffic across it, nor do devices on either side of the bridge know to use the bridge link.
At the very least you need to configure ARP so that the Mac responds to requests for devices on the other side of the bridge - i.e. when the device on WiFi sends out an ARP request for the router, the Mac responds, even though it isn't the gateway machine.
You could use proxyall to have the Mac proxy all ARP traffic across the bridge, or add specific ARP entries to the ARP table.
sudo sysctl -w net.link.ether.inet.proxyall=1
You might also need to enable IP Forwarding:
sudo sysctl -w net.inet.ip.forwarding=1
With the usual caveats that sysctl changes like this are transient and lost at reboot - add them to /etc/sysctl.conf to apply them at boot.