The original poster makes two errors. Ryanair has not withdrawn from Valencia (save for a temporary closure towards the end of last year). For example, there are currently two daily rotations out of Stansted.

Second, BA has never flown to Valencia, although BEA probably did. GB Airways commenced operations right at the end of 1990 and was on and off the route after that point, latterly as a BA franchise.

Loads on Ryanair have been variable - hence the airline putting pressure on the regional government, the Generalitat Valenciana. Off peak I've flown into and out of Valencia with as few as 50-70 other passengers (on an 189 seat 737), and this has happened quite frequently. This explains why in the last few years I've paid (on average) just £20-£30 return. Even at these prices seats were not selling.

So even though Valencia is a wonderful city, I'd have thought that with BA's cost structure it would be difficult for the airline to establish a viable operation. Events such as the European Formula One grand prix and the Americas Cup are obviously not enough to sustain even seasonal flights, although holidaymakers heading to the northern Costa Blanca might prefer Valencia to Alicante.