The nail has been squarely hit on the head. South Wales is a poor area.
You need lots of businessmen on domestics and lots of second home in the sun owners on the Med runs to make a really good low cost airline base. Bristol has both in abundance whilst Cardiff does not.
Its not the fault of the Welsh assembley nor the managers at either airport.
It doesn't matter a jot about what the last 15 miles of road is like to either airport either. Battling your way into Heathrow or Gatwick is often misery and even if the motorways are flowing you are still going to end up in car park Z5 miles from the terminal - unlike BRS and CWL.
I can't see how anyone other than members of BMI Ops planning dept can say that this aircraft/route withdrawel is either temporary or caused by a 'lack' of aircraft available. Doesn't make sense - sorry. If the route makes money why annoy all its users by withdrawing it for a while? If you really need another aircraft then there are plenty of pilots in the group available and the leases on B737-300s are on the floor with aircraft - available tomorrow - currently parked in Bournemouth....
Cheers
WWW