The DoD cancelled the LEMV project with Northrop Grumman and HAV mainly due to macroeconomics and the politics of US National Debt at the time. The Obama Administration swung the axe, the DoD chose the cutting block. Programs that were viewed as not being strategically important, such as this, for reasons outlined by another poster above, were axed. Records show that not all DoD stakeholders agreed with all of the decisions, and this one was no exception, but cutbacks had to be made nonetheless.
Ironically, the climate of resource constraints allowed private companies to take advantage to the detriment of the US taxpayer; HAV repurchased the LEMV project for just $300k, despite reports of it costing upwards of USD $100m by that stage (admittedly not all aspects of the project were included in the sale).
The economic case has not yet been demonstrated. Nor has the operational one. And there is no obvious demand for such a vehicle. However, only father time will tell and it is worth highlighting that the AirLander is not, as some posters suggest, a rerun of yesteryear. This is brand spanking new technology, never before attempted, never before utilised, and quite possibly never to see the commercial light of day. But AirLander is no AirShip! The 2001 patents are clear on that aspect (at least!)...