This is speculation. In one of the mission orders for the Atlantis, there is a diagram of an Excelsior-class starship. It's possible that the two may be connected. If so, it may partly explain why this class of ship is so prominent. The registry of this ship is NCC-72007, which might imply that Excelsiors were still being built in the 2350s and 2360s.
My not-in-any-way-canonical take on the seemingly inappropriate high registration numbers is that a)Starfleet keeps a number of older vessels mothballed, b)SF refits them when a temporary need for more ships arises, and c) many of the numbers represent reactivated Excelsior hulls in which the original names have passed on to newer vessels.
I don't see why Starfleet wouldn't build new excelsiors though. The technology didn't change in the last 80 years. Sure the existing tech has improved, but there was no revolutionary new technology in play. Galaxy class is projected for 100 years...
If Lakota can be upgraded to be able to match a defiant class in firepower, why not keep building them from ground up?
Until Sovereign class was built, which ship would fill the roll of excelsior better than excelsior?