It is Unite that have withdrawn the ballot not Bassa and Amicus.
Unite don't want it to go ahead because Bassa and Amicus have both recently said they will encourage a NO vote. Unite don't want a NO vote for the offer because that would make it hard for them to deny Bassa and Amicus another strike vote.
Unite know that it is an ok offer and they don't want a strike, particularly at Christmas, so this is a delaying process. By withdrawing this ballot they are preventing Bassa and Amicus having time for a strike. Bassa and Amicus are both upset about the appendix letter which prevents them from going to court. (details of it can be seen on Uniteba site which is Amicus's site)
With Bassa and Amicus both recommending a NO I can tell you that a lot of crew would have voted NO and a ballot for a strike would have been hard for Unite to refuse. You have to remember that most of the moderate crew, like me, have now left the unions, so a large NO vote would be inevitable. You would be amazed at how many crew STILL believe everything that Bassa says and the crass way Mixed Fleet has been introduced with the Hats issue has just managed to upset all crew not just the militant ones, even more.