The fundamental problem on this quasi-forum is that people are missing the forest for the trees.
Someone here wrote that the OP is speculating as to why this project was cancelled and that it was due to lower future profits. Another wrote that Chicago is a shell of its former self, and therefore, there is less demand on the bridge. Both comments are built on false premises. Hear me out.
The private freight railroads within NAFTA are essentially toll roads that get to set their own tolls. That's what they fundamentally are. Your actual toll roads have a great deal of government oversight and can't set tolls willy nilly, or shut down sections of toll road, or shut down lanes, to boost profit PSR style.
Until the Staggers Act was passed, the government had to approve the toll rate charged by the RR and also had to allow railroads to shut down lines, i.e. lanes. They had to do that, because a long time ago, before the free interstate highways were built, the railroads were the only way to really move people and freight and they used their power to overcharge customers and squeeze us dry.
Once Uncle Sam built the Eisenhower interstate system, which is essentially free to use, why would anyone spend money on a steel toll-road? So the railroads went bankrupt.
The problem is that we have a national freight transportation system. The interstate highways, US routes, toll roads, freight, and commuter railroads do not operate in separate silos. The railroad is the most energy efficient way to move people and freight per gallon of fuel. When the railroads went bankrupt, that meant more trucks on interstate highways intended for medium and short trips, thereby clogging those highways, generating pollution and wasting precious fuel. There are industries like coal, petrochemicals, and aggregate mining that are absolutely made for being hauled by rail and would overwhelm highway structures.
So, the government passed the Staggers Act. The railroads got to set their own tolls and even could shut down loss making lines. The railroads could unashamedly exploit their monopolies over captive industries, their bread and butter for making money. However, the unwritten expectation was that those profits would be used to upgrade the national freight railroad system and eventually grow it so that the overall national transportation system would use more fuel efficient trains and slow down the unsustainable growth in trucking.
Outside of NAFTA, railroads are just like highways, government owned. There is nothing fundamentally wrong with that government owned model unless you think you should pay a toll to a private company every time you get on the interstate...
UP's profits are often a facade when looked at from the perspective of the national transportation network. UP forces state level Departments of Transportation to comply with unyielding demands when a new overpass or highway is built over their tracks. Caltrans, for instance,had to shut down certain major highway improvements because UP would not allow a certain column in their yard, and would not even consider shutting down traffic on a few tracks to improve an interstate used by millions. This type of story repeats itself in every state UP crosses.
Then there is passenger service. Your highway is free and your gas tax is not enough to pay for it. So, your highway is heavily subsidized. Passenger trains are subsidized too, and the goal is to take people off the highway and put them in a more energy efficient train. Maybe they'll enjoy the ride too, instead of gridlock.
Well, UP does not work well with passenger service. It won't cooperate with California high speed rail, it puts Amtrak trains behind schedule as they have to wait for freight trains to pass, and it just fired a bunch of mechanics working at Metra operations.
In other countries, a bugbear these days being China, this categorically does not happen. Holistic decisions are made and the government owns all major transportation assets. So when a new highway interchange is built, or conversely a new railroad yard, assets are moved around to maximize overall utility. If a column has to go in the rail yard, fine, that will happen, rail traffic will shut down on a couple of yard tracks which is really no big deal in the big scheme of things. In the US UPRR pulls the private property card and tells the DOT to f-off, and that there is no way critical rail traffic can be put on hold...nevermind the fact that PSR will shut the whole yard down in a week. Likewise, the DOT gives UP the finger if a rail expansion involves moving a piece of interstate...which it almost never does, but I'm trying to be fair.
When you consider those hidden costs that UP incurs on the overall system and you factor in the reality that Uncle Sam gave UP their land in the first place...which is another story... how much of a net profit does UP really generate for the country?
Going back to the bridge. This bridge is on the transcontinental route paralleling I-80. We will be in an economic apocalypse before this route will get less than 20 freight trains a day. The bridge is over 100 years old and you have to go over it really slow because it is a swing span to boot. Outside of the US, such a bridge would be in pictures in a museum. Here, we run freight traffic at a snail's pace on it and will continue to do so until it breaks in an emergency, or jams open or jams closed...which is always funny.
Staggers Act envisioned that a virtuous cycle would develop where UP and their like would make big money and take a bridge like this, replace it, triple track it, advertise the higher speeds and reliability, grow the business, and put more trains on more rails. Instead, a death spiral is in place where UP sweats the assets, plateaus or lowers the business, and increase earnings per share at all costs... because UP can do that when there are only four American Class I railroads.