Anything I can come up with would be speculative, but here's my take:

• The talk around the picket line was that the bargaining group for the Treasury Board was really good at playing hardball, and the union may have felt they weren't going to get a better deal.
• The strike pay battle chest was rumoured to be about $40-$45 million nationally, which sounds like a lot, but at $75 per member, per day, it's exhausted in 1-2 weeks depending on how many people actually hit the picket line. At eight days, (for the TB group at least), I could see the union wanting to start wrapping things up.
• The ratification vote required that you either vote to ratify or vote to not ratify and go back on strike. People may not have necessarily liked the deal, but there were likely many not prepared to give the union another strike mandate.
• The deal includes the pensionable bonus plus near two years of retroactive salary increases. That's money in peoples' now (or in the coming months at least). People are hurting these days, and that sounds a lot better than a mythical percentage point or two additional raise maybe 6-12 months further down the line.