It has exceeded its expected lifespan and needs to be replaced. It crosses a sensitive environmental area and university on one side, and one of the wealthiest neighborhoods in the state on the other. And it carries huge volume of traffic.
This should go well.
The Washington State Department of Transportation is trying to get out in front of the dispute and remind people that doing nothing (which is all Seattle ever wants to do) is not an option. So they put out two videos projecting the destruction of the bridge.
They're actually pretty cool.