To that extent, BASSA have been a bit unfortunate (initially) in the BA case - they DID get a mandate for strike action. It's just that most of the crew ignored the call.
There are certain events that "set the scene" for a number of years. There was a strike by CC in 97, where rather than actually striking most crew went sick. This had the same effect as a well supported strike and crucially BA caved in. This set the scene, for the next 13 years of CC IA.
It created a belief within BASSA that BA would give in if push came to shove. It also created within the mind of a lot of crew the belief that a vote for IA would make BA think twice and crucially, that they would probably not have to actually strike themselves. This disconnect between the act of voting for IA and actually carrying out the strike has had a major influence on the events of the last 18 months or so.