It is being argued that these losses aren't just vanilla trading losses. They arose due to technical glitches at NASDAQ which led to quotes being unavailable, delayed processing order cancel requests, missing acks, etc.

Essentially, traders couldn't act in time to react to the market due to NASDAQ's troubles.

Edit: I should also add that Citi, Citadel, etc. were acting as market makers - they don't have the option of holding the stock for recovery as others in this thread suggest.