Reason is simple. People wanted an endgame TOS Constitution, not the JJ/AR/KT Enterprise. And after years of asking for it, STO gets "another" Constitution. Some people is going to be pissed off, assume it, as they feel cheated or laughed off; they've been asking for a ship, they don't get it and, instead, other people get…
Since skill revamp, cannons and beams have same damage drop off at the same distance. So, basically, what you must consider at this point is: do I want to be spraying damage all over the place (beams) or do I want to focus damage in a narrower arc against fewer enemies (cannons)?
According to novels, cannons are a Vesta class ship "canonical" loadout, as it uses an experimental type of phaser emitters similar to those from the Defiant (which happens to be "cannons" for Cryptic). For the OP, it seems to me a logical decision, from Cryptic side, not allowing DHCs in a cruiser because of its low turn…
Basically, because we don't care about it. It was slow, it was fast, who cares? We are now looking at those shiny specialization trees and those specialization points at 160,000 XP each (once you hit level 60).
Well, seeing how succesful this thread is being (and the countless laughs I have with some sigs), here goes my small contribution. See sig below :D PS: Or not... PS2: Maybe now...