Where are all the ships?

[Rynn]

Expensive in the sense that they require a lot of void motes for their engines and the archai don't hand them out readily to lower beings. In the post scarcity economies of OA most things are very cheap because, as you say, dumb mass is everywhere and autonomous replicators are old hat tech. But there's nothing the project can do to get more motes other than wait for their archai patrons to donate more. The NB article mentions an S4 void factory in operation in the system, this produces 1 mote per day. Each ship would need thousands so the cost is the total output of an archai's void forge for years on end.

In the Inner Sphere maybe most systems are connected but overall only a few million systems are. That sounds like a lot but Terragens are very prolific colonisers. Pretty much every star within the sphere has been subjected to some colony effort.

RE inter-galaxy colonisation the timescales involved kind of make any plans moot. Long lived generation ships would likely suffer some sort of social or technological breakdown in the journey. A very redundant sleeper ship might make it but there's no guarantee that the wormhole its carrying will connect to the terragen sphere (which would be millions of years old). A comm-wormhole would actually be a risk as you could get attacked from a Blight or something empire ending like the hypothetical Dawn Hunters.