This was less a comment objecting to the idea of a nuclear heat source, and more that "why not just" is a comment that fails to account for all of reasons the experts involved probably considered but decided not to "just" do that.
Why not just a nuclear reactor is a huge version of this, because obviously there are a lot of additional expenses and concerns when you deploy a nuclear reactor anywhere.
And of course the small detail that they had a reactor a McMurdo, got rid of it because it was less reliable than fueled generators, and had a massive cleanup mess to deal with because the damn thing leaked.
