There's no guarantee on a return on investment. Especially not if the nuclear power plant isn't completed and brought online.
You obviously have not been paying attention to how utility regulation works. Their rates are set by law to guarantee them a return on their investment.
If there were viable alternatives available today then we'd not be seeing growth in fossil fuel burn rates.
See above. Utilities get a guaranteed return on their investment once approved. They are generally approved based on cost, not emissions. And they are getting push back on approval for new gas plants precisely because battery storage is becoming economically competitive and has lower emissions.
You are right, if you are going to use renewables to replace fossil fuel it will require storage. For base load, natural gas is currently still cheaper than batteries and certainly cheaper than nuclear power. For peak power demands, batteries and solar are already cheaper than building a new gas peaker plant. But natural gas still provides a larger investment return for utilities.
The USA started from nuclear power being largely only a theory in 1955 to mass producing them by 1975.
A lot has changed in 50 years. You might have noticed the United States manufacturing sector has shrunk considerably and hasn't recently geared up as the center of production for a world war. The shift to nuclear power for electricity was driven in part as preparation for a third world war. Moreover, if you look at some of the outcomes from that effort, you will find all sorts of environmental and other issues that were not addressed that were justified by national defense. Like permanent waste storage.
In addition there were plants that were later closed because of faults in both construction and operation. Cost and quality control were moving targets and would be again. I don't think you will find a single nuclear power project that ever came in under its initial budget. They turned out to be far more expensive to build and operate than any of the mathematical models predicted.