A bridge for deer isn't any easier to build than a bridge for pedestrians, even if you don't care about deer being on a bridge that collapses there's a highway underneath. Cars would be crushed and traffic disrupted. So we're just talking about a bridge. It's built to the same standard as any other bridge. (Also it's more like a bridge for mountain lions but whatever.)

If the Empire State Building had been built across a highway, and had to schedule construction around avoiding disruptions to traffic, than it would've taken three years too.

We went faster when human life had less value. It has more value now, both in labor time (and therefore cost) and harm potential/reduction, so it takes more time and money than it used to. Similar story about disposable workers when the Hoover Dam was built.

We should expect this math to continue as prime working age cohort shrinks over the next century due to structural demographics.

For deer? It's much more for the endangered wild life like mountain lions. I loved in so cal and we had multiple passes like this and it was incredibly helpful in maintaining the mountain lion population

5 people died constructing the Empire State Building.

0 people died constructing this bridge.

I guess if you think working class people's lives aren't important then the human cost doesn't matter to you, but for non-sociopaths it does matter.