Makes sense. I think there's ample evidence that the Federation grew significantly in the years prior to TNG. Just look at how many start-up colonies and outposts the Enterprise visited over the course of the show. Starfleet must have been stretched a bit thin and would have been more concerned with getting as much use possible out of existing designs.
Another thing worth considering is the advent of replicator technology. Starfleet in the TOS-era seemed much more concerned with securing resources than in the TNG-era. Replication must have made some parts of starship production cheaper and easier, even if some components couldn't be replicated. Maybe replicators made their appearance sometime between the Ambassador and Galaxy classes, and that's part of why we see Starfleet experimenting with bigger ships and a much wider range of designs?