I see little use for a nuclear-missile-equipped gun-heavy expensive superweapon in peacetime.. (But i think the novell does make mention of morningstars). Besides, It had issues with it's unstable jumpdrive.
I would be careful not to place too much emphasis on the jump drive. Like the Phase Transit Cannon being decommissioned, it's more of a joke than some universal deal breaker. Complex mechanical products always have bugs in the testing phase. If the Morningstar became a frontline fighter, they would have fixed a bunch of things along the way.