Nuclear fission is a stable source of energy that does not produce carbon emissions in production. It's pretty much the answer to the climate crisis except that it produces dangerous waste that is horrendous to store and manage.
Fusion mainly avoids this :)
But the main problem of fission is that it's too damned expensive, with very large capital cost. Fusion makes this main problem worse, not better.
I'd be interested to know which fission plants make fuel recycling and waste disposal trivial, I could make a lot of money!
In reality, even the gen 4 plants that have interesting approaches to reprocessing still produce a lot of harmful radioactive waste. Not all the fuel can be recycled and the process itself is imperfect and messy.
You might ask why fission reactors aren't designed that way.
The trick is that something like 10% of a fission reactor's thermal output continues for many hours due to decay heat, whereas with a fusion reactor that can be orders of magnitude less, with appropriate material choices.