I fail to see a reason for what you are asking.
I get that we all find ourselves on different sides of the realism debate from time to time, as what seems realistic to one person, may break immersion for the other.
The only thing I can think of, is that sometimes shipyards can spawn in odd places, and if taking in-game distance literally, appear just as far away as neighboring planets(Mars like).
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But since you can move the production slider to building or ship, I fail to see any difference between wether the game makes you build a colony ship or lets you build a project on the home planet to colonize close neighbors. The whole system just seems redundant, perhaps confusing to newer players.
But that's my opinion, of course.