That's totally backwards. The short version is that due to advances in manufacturing and metallurgy, there is no longer an advantage to scaling manufacture beyond a relatively small point. Economies of scale is not really a result of economic forces; it's dominated by engineering and other realities.
Look at how Alcoa revolutionized US manufacturing by making large numbers of small-scale rolling mills instead of large mills. Look at how the heavy press program[1] has fallen apart. Look at how large nuclear plants must now be made globally, because no single country can even come close to manufacturing the whole thing themselves.
Global manufacturing no longer has government investment driven towards the heavy presses required to create massive reactor vessels. Industries have figured out how to use welding, alloys, and smaller forgings to improve their products- both strength to weight and cost. Making big reactors nowadays is like an Apollo program, and subject to the same far higher one-off costs and inability to amortize.
In a market with strike prices and capacity markets this may not be a serious issue though. The best is the enemy of the good. Particularly when you are investor who wants to see a return within the decade.
Going smaller will shoot the price through the roof. The basic convention is the bigger reactor you have, the cheaper it per unit of power output.