Does anyone know why SeaTac chooses to de-ice the planes at the gates and not on the tarmac while they are in line for take off like they do in Canada? Planes can't get out of the gates. Then inbound planes can't get into the gates.

Because its their SOP, safety and more convenient to get it done.

I live in Alberta Canada , and they spray the plainest here when it's by the gate cuz its states on the plains surface for a while and don't need to re do it again it's just to prevent the ice build up , I'm not a professional just my own thoughts

It's my opinion as an airport deicer in Albany, NY that the proper procedures just were not in place and no one knew how to handle the situation. I feel like it was a failure in management to train their employees for deicing events. These kinds of snow and ice delays are unthinkable where I am from, the moment the snow stopped at 11am, things should have moved very quickly and they just didn't like they had to direction or orders from their superiors.