I like to offer an idea of mine witch is bothering me for some time.
I have 12 chars and most of them use special ships either from events episodes z store. Some have nice looking bridges like the Galor, Obelisk, Dyson, Plesh Brek. Other like my Kar'Fi use standard bridges i am sure its not only the Kar'fi that dont have its own unique bridge. I know designers are always busy but consider this i wold be more that wiling to get a Kar'Fi bridge from the store to make it complete. And i am sure i wont be the only one. I am sure Caitian Atrox and few other dont have there own bridges i am not even talking about a full layout but a bridge similar to the Jem hadar Carrier or the Scimitars.
"Jolan tru, from the Mirror Universe Romulan currently a Federation Ambassador to Mol Rihan"
Bridges/Interiors take far longer to make than ships. As such, if there is sufficient reason to make a full ship interior (such as the newish Romulan Ship interior, being used all over LoR) we'll make one. If there isn't, we won't. Making a custom bridge, let alone a full interior for the Corvette (while cool) would be a significant investment of time/resources. So, we could have skimped on Risa more, and built an interior, or done what was done, and skipped the interior which would have served little purpose anyway, and went with beefing up Risa.
Building custom bridges takes longer than a couple of days. Something like the Suliban/Andorian/Tholian Bridges, were each 5 days of Environment work from me. Then it needs design time to hook up any interactables, doors, etc.
Doing a full interior is significantly longer (i.e. 3 weeks to a month)
The Breen cruiser didn't initially come with a custom interior but they hooked one up when they made the Breen Plesh Brek raider so you never know. Maybe after whatever current project they are working on they will have some time to make a awesome interior for the Risian ships and some others but only time will tell , till then i just enjoy the ships and play the game as I have for the last 2 years.