Thermal storage is harder to integrate with renewables because you need a recovery mechanism, i.e. a steam turbine. Because nuke plants already have the turbines, it’s cheaper to collocate the storage there. I could see a future where the nuke and fossil plants are converted into thermal storage facilities without the boilers to reuse the existing turbines (and permits to operate, and interconnection agreements).

renewables with a recovery mechanism is still simpler engineering than a nuclear plant.