A common misunderstanding arising again in discussion here.
The term 'LOW COST AIRLINE' is not and never has been a reference to the fares which customers pay. The term quite literally means that the inherent cost of operating the business is kept below those of traditional legacy carriers. This is achieved via the way the business is structured. What the customer actually experiences is a 'NO-FRILLS CARRIER' ... an airline which compartmentalises every aspect of the flying experience and charges by component of the itinerary ... add-on fees for all 'frills'. Note that whilst fares offered by these carriers often are attractively priced, they don't have to be. There is no implied promise that all customers will pay a low fare. These carriers are businesses which exist to maximise profits, and they do this by deploying yield-management software to maximise revenues like every other airline.
Of course, the public have come to believe that a 'low cost airline' means low fares for them is part of the deal. It really isn't. The airline will charge what the market will bear. But, of course, the LCC's are quite happy that this widespread misunderstanding is commonly held by the public at large. If customers have convinced themselves that 'Airline X' will always sell them a cheap ticket, the company is not going to disabuse them of that impression. The myth serves them well. So customers find out the reality the hard way when they look to make a late booking on a popular route.
If you're an investor in an airline, you want to see 'low costs'. If you're a passenger, you want to secure a 'cheap fare'. Two very different things. The one does not guarantee the other.