Poaching, as you call it, isn't always what it seems. Once a member sends a request to another club he/she is prompted to quit his/her current club and does so.
I've owned 3 CC's here and never criticize any member for moving elsewhere. I have even closed 2 of them (fairly large) due to lack of participation.
Problem is, many players just don't participate in CC events and some that do, get tired of losing to the same players over and over again because the CC's create tournaments for all members and not tier specific, therefore the member seeks out other clubs.
Another issue that causes players to change addresses is Rules - Do this - Don't do that - You are not allowed to do anything without clearing it through club directors first. etc, etc. Some CC owners treat their clubs like Kingdoms rather than the social environment it is intended to be.
Now, with the addition of CC passes and special glory awards, players seek out the enormous clubs in hopes of being awarded some sort of recognition for their efforts.
When all is said and done - it's a member's choice to do as they choose.