Because what is true for these 3 countries is not true for all countries. There are counter-examples where nuclear is cheaper.

In most countries which don't have the advantages of Australia or Finland, you do need a mix as the OP was saying

I didn't downvote but it's nonsense, nobody can sustain a winter with batteries and other storage.

I only checked the first paper and it doesn't seem talk about what would happen if a 3 weeks bad wind event would happen in winter, and a rough look at the figures makes me think it just wouldn't work at all. I didn't check the other papers.

And the proof is in the pudding anyways, if it's that cheap and feasible to do, well let's see who's doing it.