Frequency of flights in a given market is a huge selling point for any airline that can afford to offer it. This is how PSA and AirCal, and now Southwest, took over all the major intra-California routes.
If a market can support high frequency flights, that market can easily end up in a "winner takes all" situation with one airline providing 90% or more of the flights. The airline needs deep pockets to get to that point, and then comes the hard part: The airline needs to resist raising fares unreasonably. Higher fares entice new entrants to try de-throning the market champ. Low fares discourage new entrants. Southwest Airlines knows this story, because they've done it this way since their early days flying within Texas.
JetBlue's route structure is poorly matched to paying this game. Therefore JetBlue is better off avoiding markets that can support high-frequency service. The E190s could have been a game-changer here, but JetBlue apparently does not want to use them that way.
The only time JetBlue has done this and succeeded to a point has been the NYC-Florida routes. DL no longer flies EWR to Florida. Continental dropped their fares. Etc, etc, etc...
It seems like that JetBlue has been more interested in putting dots on the map rather developing them fully before the next one comes on board. WN seesm to do it a lot better.