I guess it is a strong design decision from the team. Productions points can't be carried-over the next item (even if the points are not costing BC). I fail to see how it can be good on a micro-management stand point.
Standard example is a colony ship 99% complete which need one more turn to finish. The next ship will restart at 0% completion thus.
In such case the player have two options, depending of his willingness to commit into tedious micro-management: 'laissez-faire' and pray he will still win without optimization, or tweak settings, planet by planet, turn after turn... I guess that for players playing at suicidal difficulty, they even create custom ship design on the fly, to have the production fall right and not lose a turn!
So... why? It is trivial from a coding standpoint and Stardock has the resources to change such things, in the end if this is not done, it means this is by design. But I dont understand how the benfits of this (lack of) decision is better than the drawbacks it inflicts on players.
Thank you for your attention.