Thing is, traditional nuclear plants generate so much power that we only need a few "bespoke" plants to fill in all baseload demand and even provide enough redundancy. Renewable sources are quite a bit cheaper though wrt. to the sheer amount of bulk power that they supply over time, it's just unreliable and highly intermittent. Smaller reactors just aren't very useful in that kind of scenario - it's unlikely that they'll be cheaper per watt than a few large plants.