This is a theory that I've always had, and I wondered if anybody else on here had come to the same impression.
We only saw this ship in two movies -- ST V and ST VI (okay, and technically
the end of ST IV
). And on both occasions, the crew are pulled out of 'shore leave' (or whatever) to go on a critical mission for which Starfleet feels they are the most suitable people.
The thing I've always figured is that NCC 1701-A and her crew were always
in a state of semi-retirement, right from the moment they were cleared at the end of the fourth movie. Effectively, the 'new' Enterprise was already mothballed even before ST VI began, just as Admiral Morrow said would happen in ST III, but I reckon the crew remained on the 'active duty' roster only in some kind of backup capacity, where they could be called upon if needed but were otherwise allowed to do whatever they liked. The reason we see the crew bumming around doing whatever at the beginning of ST V, and likewise they all have to be collected together from different assignments at the beginning of ST VI, is because by this stage in their careers they are no longer a regular crew staffing a regular ship. Starfleet can still recall all of them from time to time though, set them up with the Enterprise, and send them out on some adventure or other. Hikaru Sulu is of course an exception to this, having accepted the commission as commander of the Excelsior.
I think this helps to explain why the lifespan of this particular Enterprise is so short -- it isn't really
an "active Enterprise". Obviously under this hypothesis some other vessel (the Excelsior?) has taken the mantle of being the actual flagship, and of course NCC 1701-B is probably under construction during the time-frame under question.
What do you reckon? Personally, I think this seems more plausible than it would be to assume that Enterprise and her crew were actively
undertaking regular missions during that short period of time, and at that particular stage in their careers.