BA and the like are unreliable, expensive, and have proven they are not great when things go wrong. So people will move to the LCCs - yes, they may not be great when things go wrong either, but the lower cost of the ticket compensates for this.
LCC are utterly useless for business travellers and that is where the money is, especially now that the fuel price makes such a big part of the cost of flying.
LCC's don't fly to the correct airports - when your employees are costing £40-200 per hour, you will not want to waste their time getting to Stansted.