They don't have to actually sell a single scratchcard for it to be worthwhile for them - the whole point is to cheapen the experience.

They have an entire theory of marketing based on people believing that "if it feels cheap, it is cheap", and so they deliberately build in a bunch of annoyances (scratchcards, arbitrary baggage restrictions, checkout hoop-jumping, endless PR about removing toilets or running standing-only flights) which serve to make their service seem as cheap and nasty as possible.

And it works: some people simply ignore the nasty aspects, others are willing to put up with them in order to get a bargain, and yet others actually take pride in wading through the crap - usually expressing it in "I beat the system" terms. And here we are talking about it on a barely-related thread - carrying their marketing message further!