Two things
They settle on a design and then don't keep fiddling with it - their designs are also evolutionary and not revolutionary and they are willing to comprise and accept 90% of what they'd like to get on 100% of the ships delivered on time
they build (and finance) at a steady tempo so the yards keep their skilled men, the managememnt aren't always on a learning curve and the manufacturing company isn't tempted to draw out building to prolong profits