BA discovered, along with the rest of the airline world, that not enough people will pay the price. Over the last 30 years pricing in numerous areas of commerce has moved to the pricing formula of a certain well known LCC. People have decided that they want the headline price to be low and might then pay for extras. This has been tested many times, one simple example is motor cars. The low priced threshold of a lease got people to take new cars which, ultimately, cost them more.
BA, along with the rest of the legacy carriers, cannot readily be two carriers. The example of LH and Eurowings is instructive. However, this combination of Legacy and LCC will continue in one form or another.
Each and every purchase, be it a car or a plane ticket or a take away meal, is decided upon at the time at the price on offer.