KK,
I think the recruitment ban must be viewed in context. It is my understanding the ban is a predetermined reaction by IFALPA to CX's actions in terminating the contracts of the 49ers.
When examining the dispute at CX, the details are amazing complex and the recruitment ban is but a tiny part of the overall dispute. Whilst I appreciate to an outsider or new-joiner, particularly one who bases his/her opinion solely on pprune, the recruitment ban must seem a big play by the AOA. It is in fact only part, and perhaps a small part, of the overall strategy the AOA has adopted.
To answer your question, the AOA hopes to put enough pressure on the company that it will return to the negotiating table and negotiate in good faith to achieve a deal with the pilots. The ban compliments the other pressure points of extensive global litigation, limited industrial action, appeals to HK CAD to name but a few.
CX pilots are acutely aware that there are no "silver bullets" and nobody believes the ban will prevent new joiners. However, it does signal to CX management, in the clearest possible terms, that the body purporting to represent the views of pilots', internationally, disapproves of CX's actions. At a more basic level it will limit CX's selection process and lays the foundation for further actions in this area such as training and upgrades bans.
All of the actions the AOA are taking have considerable downsides and the ban is no exception. The AOA membership has taken the decision, overwhelmingly, that the downside of doing nothing far exceeds the downside of the actions they are now taking.