A bridge is not a HUB. A bridge is a SWITCH. A bridge will not blindly pass all traffic… it will only pass traffic that is destined to somewhere on the other side of the bridge.
There probably isn’t a way to send mirrored traffic over a link like that. You could route your entire ether1 link over the link and then do the mirroring on the other side, but that probably isn’t ideal.
Cisco has RSPAN which does remote mirroring, but I don’t think mikrotik has anything like that.