It really isn't "only" Carnival.
The Royal Princess had an engine room fire back in 2009. The Azamara Quest had a fire in 2011, the Costa Allegra also had one in 2011.
The worst fires have been on the SS Norway (NCL) when the boiler exploded and killed six crew members and the Star Princess in 2006 where one person died of a heart attack triggered by the fire.
Then the mechanical breakdowns of the Millennium class ships. I think all of the ships had failures in their Azipod systems and one ship did most of their Alaska season on one engine and an altered route.
Every cruise line has had mechanical failures and accidents. Right now Carnival is in the cross hairs and if something happens everyone hears about it.