The cost of operating suitable equipment is one factor in its failure.
So what would be suitable equipment in this day and age for low cost longhaul? There is a market for it but under the right conditions, ie departure airport, slots, destinations and of course aircraft.
The only carrier that seems to be working so far is Scoot which caters for the high density Asian market. If they were to spread their wings to Europe would they be able to make a profit? Time will tell.