system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why are there so many Miranda and Excelsior class in the 24th Century, but no Constitution refits from the same time period?

I was watching the Dominion war documentaries and noticed an abundance of Miranda class and Excelsior class ships but no Constitution class ships. I have read engineering texts stating that the refits were redesigned from the keel up to be the back bone of the fleet. Was there a flaw in the design or did Starfleet just not build that many?
gpt
Some Constitution-class vessels survived in active service well into the 2390s, but they are considerably rarer than the much more common Miranda-class ships of the same era. This is due to a number of reasons. Constitution-class cruisers were usually deployed on high endurance, long range missions, spending years or even decades without refit or repairs. They were hard-working ships and they showed it. After many years of being on the frontier, many Connies were just too worn out for continued service. It was easier to replace a worn out Constitution with a brand new Excelsior than it was to repair and upgrade.

Additionally, the Constitution-class cruiser was built as a top of the line ship of its day (the 2250s). Some compromises were made for the sake of performance. Connies were never comfortable ships, with little thought put to future upgrades. During their midlife refits in the 2270s, the Constitution-class cruisers had to be significantly rebuilt to incorporate the newest technology. Many were just replaced instead.

The other major reason why the Constitution-class cruisers weren't retained in as many numbers as the Miranda-class ships was because of the Miranda-class. By the 2320s, as the bigger Ambassador-Class and the Celestial-class ships entered service, the difference in capability between the Miranda-class and the Constitution-class just didn't justify the additional cost of the Connie. The Miranda-class was the low capability low cost (in maintenance and manpower) frigate designed to accompany the high capability Constitution-class cruiser and perform duties that didn't warrant a capital ship, to free up said capital ships for other missions. The Mirandas hadn't been sent on long deep space missions and received by-the-book maintenance at Federation facilities. They were just in better shape than the Connies, so they've lasted longer.