If they ran it, I'd say there had to have been a reasonable prospect of success The Dones aren't fools, and they will have weighed this very carefully**.In which case they must have had very poor legal advice to take it that far.
It absolutely won't have looked like this to the outside world, but for the industry it was an important case where a punter benefited for an accepted error and profited beyond their own expectations and the parameters of the game.
Consider the parallel with a mispriced item on a retailer's shelves, say a TV for £100, not £1000. Fortunately the law of contract gets the retailer out of jail there, as it does online, too, if a manifest error has been made - we've all seen the cases. Here, the only reason that the action succeeded was because the Terms were badly written.
**As in, they knew the sh1tstorm that would happen (is happening!) if they lost - and perhaps if they had won, too.