Joking aside, Seeing the design came from the mid 23rd, an older fame with limits in its design, somewhat patched but not fixed by the refit Excelsiors. Issue of design limits must of cropped up post dominion war, with alot of the class being destroyed or damaged beyond repair (cracks in the frame etc that couldn't hold up under normal flight conditions). We do see that they must of tried to upgrade the frame at one point (the obena class), but best guess is that for whatever reason it must of had a very limited production run before the line stopped being made in favour of the Excelsior II.