This might have something to do with it:

The first country to have a reactor could “declare a keep-out zone which would significantly inhibit the United States,” the directive states, a sign of the agency’s concern about a joint project China and Russia have launched.

Unexpectedly, it doesn't seem like this is a primarily technical decision.

No sunlight for 10 days at a time.

The previous 40kW proposal linked in the article mentions it would allow operation where solar panels aren't feasible, like permanently shadowed areas where water might be. There's also the dust problem to solve with solar panels, although this would also be a problem for nuclear reactors since their radiators could become less efficient from dust buildup.

There's a lot of extra costs associated with making solar panels space worthy. No atmosphere also means no radiation shielding and no cooling. I actually managed to find satellite solar panels for sale: https://www.cubesatshop.com/product/solar-panels/. They have front and back panels but if we assume they didn't have a back and all panels faced towards the sun it would be ~120W. That gives us $133/W, which means 100kW would be $13.3 million. Unfortunately the mass isn't listed, so we can't estimate the launch costs. I don't have a way to estimate the cost of a fission nuclear reactor on the moon since we don't know how it would work yet, so this calculation is mostly for fun. That math would change significantly if we are able to manufacture solar cells from lunar regolith.

In nuclear's defense, we've been sending plutonium-238 into space since 1961. There's been a few accidents, but the fuel casing has been improved so that the later accidents resulted in no leakage. That was in the early days, so we know a lot more about safety now. Do you think the risks are too high for any nuclear fuels in space, or does uranium pose unique risks?