Apples vs. oranges; this was an straightforward emergency replacement job on a major rail route, not a complex project that has been in planning for several months, so it's not at all surprising that this took so little time. As others have pointed out, UP had pefabricated components stockpiled and ready to move and a list of contractors handy in case something like this happened; the railroad was prepared for this and thus was able to move quickly. As you've said, it's not over yet; there's still a fair amount of cleanup work to be done, and that won't be finished as quickly.

Also, government projects (and public works projects in particular) tend to affect far more of the general public that "private" projects; that naturally leads to delays, changes, and (in far too many cases) cost overruns (after all, government officials - especally elected government officials - can't just ignore the NIMBYs, environmentalists, special interest groups, and others like private industry can).