As these banks are heavily invested in fossil assets, they know that if they support the nuclear dream they will sustain our reliance on fossil. At least for another 20-30 years. As the building of nuclear power plants is so slow and usually gets delayed by more than 200% (read Flyvberg's book how big things get done) the banks know they can hold on to their fossil assets.
Now, if we move to renewables, batteries included, the movement from fossil going to happen must faster. The US is a bit slow but in many other countries the growth of EV is replacing oil consumption already quickly. In order that not to happen, these banks want to pour (our not their) money into slowly built nuclear power plants and delay the energy transition. That is what they are promoting.
Let's see if that is going to work. Nuclear power can not compete with the cheap and yearly getting cheaper solar, wind and batteries.