Segregation of duties. Pilots responsibility to deal with the engine failure, notification of the incident, descent to a safe altitude because of the depressurization, safe divert and landing.
Cabin crew (once safe to move) to deal with immediate checks of the passengers to ensure all on O2, then prioritise treatment of incident. It may even mean that they deal with general passenger panic over initial treatment of an individual passenger injury (a confused situation may obscure other issues that need priority). When finally it's calm enough they can deal with passenger injuries , liaise with the cockpit crew and plan for the landing and transfer to the emergency services.
Amazing how many think of them as food and drink servers...
