Its mostly because the process inherently is just boiling water with resource x and making steam engine go brrr. Coal plants have the infrastructure for the energy generating and logistics allready there and the parts are allready wistanding the heat. Additional bonus is that while coal plant needs weekly refills nuclear plant could produce the same energy with only few refills a year.

Here is pretty comprehensive recearch made in 2022 by DOE It takes account many benefits and hurdles if the process and its not trying to sugar coat it. (Sadly current USA political situation is not intrested pursuing this any further)

Here is good paper that studies the field wider but also aknowledges the potential in C2N conversion