It worked for them in the past, and maybe they assume it will still
Problem is, this is 2017 and the employee commands more respect. Unless there are masses of pilots ready and waiting to pick up the slack on the lower pay/bonus, then the incumbents have the upper hand and Ryanair will eventually have to give way (kicking and screaming all the way)
"Haven't had a strike before", there's a first time for everything, and maybe it's long overdue