Ok, now because I have already have understand about Miranda, Constitution and Constellation ; what about Ambassador and Excelsior? As we already know, Ambassador is newer than Excelsior, but we see more Excelsior than Ambassador in DS9 and TNG. Even Galaxy Class has more screen time in DS9. So what happen to the Ambassador Class? Is it a failed design or what?
The real reason why we never saw the Ambassador class more than a handful of times was because the filming model was damaged and wasn't used again after the first episode of DS9. Conversely, the Excelsior model (and the Reliant model as well) survived long enough to be scanned into a CGI model, which is why we see tons of them in later DS9 in CGI-heavy space battle scenes.
The in-universe reason? The one that gets bandied about the most is that the Ambassadors were built for long-range deep space exploration, and we don't see much of them simply because none are anywhere close by. There's certainly no indication whatsoever that it was a failed design. If you think it was a failed design simply because we didn't see it much, then by that logic the 20-odd conjectural designs must also be failed, because we didn't see them even once. Or the BoBW kitbashes...or the DS9 kitbashes...or heck, even the Sovereign and Intrepid classes...