“The cheapest fares must be selling like hot cakes”
Possibly because there were very few of them?
And of course people like a bargain, the marketing tactic to exploit this is called pricing elasticity and it is a well known part of the marketing mix.
Usually employed by companies who are not sufficiently differentiated to sell on higher quality than their competition.
So it seems BA at LGW cannot beat easyJet on quality and they are using pricing elasticity to compete.