How so? I am in the industry and everyone I work with take them seriously.
Edit:
Even if you refute predictions made by the IAE, nuclear is still not as expensive as other sources of electricity. For a more specific example, the University of Waterloo released this report analyzing the Ontario grid in 2017.
If you look at Table 1, you will find that nuclear costs between hydro and wind while gas and solar cost more. This is one example but it does illustrate that nuclear is not necessarily the most expensive. Things have improved for renewables since then but I believe they have for nuclear also.
"In December 2020 IEA and OECD NEA published a joint Projected Costs of Generating Electricity study which looks at a very broad range of electricity generating technologies based on 243 power plants in 24 countries. The primary finding was that "low-carbon generation is overall becoming increasingly cost competitive" and "new nuclear power will remain the dispatchable low-carbon technology with the lowest expected costs in 2025". The report calculated LCOE with assumed 7% discount rate and adjusted for systemic costs of generation.[79] "
https://en.m.wikipedia.org/wiki/Cost_of_electricity_by_source