Nobody has got this one right.
No SLC. Southwest wasn't in SLC at that time.
Initially the only flights from Denver went to ABQ, with connections to points West.
They later instituted nonstops from Denver to PHX.
No nonstops from there to Las Vegas either. Southwest was in Las Vegas but was not really a heavy hitter there.
Nonstops to Albuquerque and Phoenix only.
And passenger loads were not the reason that service was discontinued.
Southwest didn't get their own gate at Stapleton. They had to use one of Ozark's. To use the gate they had to subcontract with ozark to provide their baggage handling and ground handling opns.
Let's just say that Ozark employees did not have the same sense of urgency in turning flights and loading bags that Southwest employees customarily have.
Denver was profitable, but the citizens failed to support Southwest like they should or could have. Many were content to keep flying Continental, or United, or Frontier (not the new one).....while paying the lower fares that Southwest brought with them.
When Southwest discontinued service, thosse low fares became a thing of the past. So if there are folks out there who think "I like Southwest in my city, but I won't fly them" I might admonish them by using Denver as an example of "use it or lose it".