The Federation seems to unveil a new class of starship every five minutes these days. It's only been about seven years since Star Trek: First Contact, but in that time, we've seen the Prometheus, Centaur, Curry, Elkins, Nova, and Luna classes. Now we're meeting the Vesta class, to boot?
It just seems like the Federation's building a lot of new starship classes for a nation that just emerged from the most damaging war in quadrant history and that's still struggling to rebuild...
Well Centaur and Curry are composed from elements of older designs, so who's to say they are even remotely close to new introductions. The Nova was already in service pre-Dominion war to have gotten lost in the Delta Quadrant pre-Caretaker and is in he same design family as the Prometheus and Sovereign, the post-Wolf 359 generation. The Luna class was in development pre-war and the Vesta, if we a assume was built as the test-bed for slipstream (ie, after regular contact with Voyager) is the only very new design, and like the Luna comes at a time when Starfleet is presumably rebuilding it's forces after the heavy losses in the war. (And I've never even heard of an Elkins class)
Wars spark innovation, and the damage dealt to Starfleet will necessitate them building lots of new ships, so surely we should be seeing more new designs starting to appear by 2181.