It's not about concentrating effort. Many things are done and sit around for a long time. Remember when CBS vetoed one of Cryptic's ship designs so the offered another in its place on the date?
Sometimes they are put on hold to fill specific empty points in the calendar. For example the Vulcan ship is coming in Jan and the Andorian one in Fed even though we've seen pics of the Vulcan ship for a couple of months now. And other times they might be waiting to bundle them. I'm sure much of the Enterprise bundle was done at different times. They could have offered the ENT costume while they worked on the MU ENT costume and offered that later; and who knows when the NX was done.
Plus different items are being built on different versions of the game. There are people working on Season 3 and people working on Season 3.1 version and people working on Season 3.2 version and so on. The Troi costume might be on the 3.0 game build and the AGT costumes might be on the 3.1 game build and needs to wait for another piece of tech.
A lot of people think devs build things in specific ways but it's really a hodge-podge of stuff being built in different game versions in very different times, rather then in an A to B to C way.
The Vulcan ship costume is also in the Foundry, by the way. I already used it on my first mission (Scavenger Patrol) as a hostile. Pretty neat looking. I preferred to run it with the Breen Cruiser Group, but somehow Tetryons and Transphasics felt wrong for the other ships (and I didn't want them to attack each other, which is what happened when I gave the second ship group a different enemy group AI.) [/tangent]