I think they found in testing that players are simply risk averse. The less amount of dura, the less amount of time players will actually risk their ships. This is partly due to the grind, players don't want to risk the hours it took to procure their ships.
Crafters will have less people buying their ships, not more, with less dura, unless the grind is significantly reduced in how long it takes for players to accumulate the wealth to get said ship. At first glance, one would think ships would turn over more rapidly with less dura, but I think there is some serious underestimation of how risk averse players can be.