EasyJet are not interested in Cardiff and neither are Ryanair really. They will only come to Cardiff if they offer them a deal that they can't refuse. Cardiff Airport has spent a shed loads of money on advertising of late pushing the Vueling routes. Newspapers, Several radio stations, Wales Autumn Internationals, Ticket barriers at Swansea & Cardiff stations etc and wouldn't this all be a waste of effort and money.
I believe what is understood here is how fragile the South Wales economy is currently compared to that of Bristol and the catchment area. Yes a lot of Welsh passengers use Bristol however not enough to sustain the Ryanair network currently operated out of Bristol.
Now if Ryanair or any other airline wanted to set up then the airport of course wouldn't refuse them however why should the airport management incentivise four douplication of routes? Ryanair has a track record of threatening to withdraw all of the time however the reason why they never is likely due to the airport giving in.
Manchester initially didn't fully embrace the low cost carriers however they have now changed their stance. Don't forget the airport also has a range of other airlines which may counteract the very little fees that Ryanair must be paying.
Actually it is a matter of choice because decisions made now could impact the future. You don't plan for now you plan for a few years time. It took Vueling four years to come to Cardiff after initial talks with the airport management. If you don't think they could end up in a worse position then guess again.
We currently have Vueling and you don't know what talks are going on considering the Welsh Government have also launched a visit Wales marketing campaign in Catalonia.
2012
BCN 3 x weekly A320 (Summer season from March)
PMI 3 x weekly A319 (Summer season from June)
ALC 3 x weekly A319 (Summer season from June)
(Peak season capacity approx 1398 per week)
2013
BCN 2 x weekly A320 (Summer Season from March)
PMI 3 x weekly A320 (Summer Season from June)
ALC 3 x weekly A320 (Summer Season from March)
AGP 4 x weekly A320 (Summer Season from March)
(Peak season capacity approx 2136 per week)
Based on Vueling seating capacity which I believe to be A320 - 178 seats / A319 - 144 seats.
Vueling also offers more onward connection choices through their Barcelona hub along with Iberia onward connections which cannot be ignored.
Now if you invite Ryanair then lose Vueling then have to increase fares eventually to make some money. Ryanair throws their toys out of the pram you would be left in a worse position because there would be less low cost airlines to step in the gap. Especially as Easyjet are not likely to be interested due to their very large aircraft base at Bristol and would dilute their own passengers.