^ Good point. There's such a gulf between the design of the Galaxy Class, and all those 'other' cold, utilitarian looking Starships we keep seeing in TNG, that it does make one wonder about the health of the Starfleet in the 24th century.
TNG didn't have the budget to make ''newer'' - looking ships for most of the duration of the show; so movie-era ship models were recycled (Stargazer was originally going to be a Constitution ship but it was modded into a Constellation at the last minute - some lines were overdubbed)
The handful of "newer" looking ships seen were most likely kitbashes from model kits of the E-D (Nebula, for example, although for GEN i believe it was digital).
So therefore, I theorize that all the newer class ships were out on extended duties and the older ''workhorse'' ships cruised closer to home. Just because we've only seen older ships doesn;t mean they're all old ships.
I know the real-world reason for it, and I'm not talking about the models anyway, I'm talking about the interior sets. There's such a diamorphic difference between the interiors of the 1701-D and those of
every other Starfleet vessel that we ever see on the show, that one is only forced to wonder why 98% of the fleet, even the more modernish ones like the Nebula Class, all seem to still be movie-era utilitarian rust-buckets on the inside, and that only the Galaxy (and arguably the Sovereign) aren't.
It's easy to say "Oh, well to save money they just kept using the 1701-refit bridge set in a variety of different permutations". The point I'm making is that all of those permutations still look like the 1701-refit bridge. None of them have the uniquely 1701-D flavor that one might expect from 24th century starships. So, what's the in-universe explanation for that?
Unless, of course, Starfleet has the same kinds of money-crunch problems as Paramount Pictures, and uses off-the-shelf parts (in this case older bridge modules) for new ships?