That argument should apply to houses as well, but building houses has become more expensive in the last 50 years not less. Generally construction does not sign

That argument should apply to houses as well, but building houses has become more expensive in the last 50 years not less. Generally construction does not significantly benifit from economies of scale, while fabrication does. Now we could build lots of small scale reactors, but while construction costs might come down (so far completely unproven) running costs most definitely would go up. You don't want to run even a small scale nuclear reactor without qualified staff, security etc..