The last time we saw any Ambassadors on screen was DS9’s pilot showing the Battle of Wolf 359. [...] This would explain never seeing them again
Chronologically we see
Ambassador-class ships twice on screen after the Battle of Wolf 359 – the USS
Zhukov in "Data's Day", and the USS
Excalibur in "Redemption II". The
Zhukov is then namechecked in season six's "Aquiel", though it doesn't appear; so we have direct evidence on screen that the
Ambassador-class was still in active service as of 2369.
Although never confirmed on-screen, the
Star Trek Encyclopedia lists the USS
Exeter NCC-26531 as an
Ambassador-class ship. She was still active as of 2374 according to DS9: "You Are Cordially Invited", and was listed as suffering extensive casualties in the wardroom personnel status lists "In the Pale Moonlight", including her captain being killed in action; so we have circumstantial evidence of at least one
Ambassador-class ship actually serving in the Dominion War.
along with some of the other wacky designs we saw that one time that appeared to be pre-Galaxy testbeds (Springfields, Challengers, Freedoms, etc.). There weren’t that many to begin with and were all just flat-out gone.
One of the most frustrating things about subsequent
Trek series starting with DS9 is that we never get to see more of these pre-TNG era ships in favour of lots of ageing 23rd century designs. While with DS9 in particular this was down to production limitations more than a deliberate decision – no complete physical models of the
Springfield, Challenger, Freedom, New Orleans etc were ever made, so including them would have been more costly and time consuming than relying on existing ship models and CGI assets – it'd be great to see more of them if DS9 ever does get the remastered treatment, especially as now have excellent CGI models of them.
Lower Decks has no excuse. I kind of wish the
Cerritos had turned out to be a
New Orleans-class or a
Freedom-class.