Maybe they've forgotten all the business they lost to FedEx the last time they went on strike in 1997.
They have very little to lose while doing a strike.
For the drivers, that is a lot to lose.
We lost almost the entire load/unload staff though. The grunts in the truck at 12am unloading semi-truck after semi-truck worth of boxes. They were only getting ~$8/hr and couldn't afford to be out for 2 weeks. Out of 12 guys on the team I supervised I think 2 came back.
Strikes are to be avoided if possible but they're a forcing function to improve work conditions, not a strategy to boost revenue.
I grew up with many union democrats around my father. A lot of them had the opinion this is a multiple million person metro if you won’t spread your gains then die off and someone else will move in.