There is no conspiracy to destroy Carnival. If things were happening on one ship fairly often then the investigation might look for a disgruntled employee. But is there a ring of saboteurs spread out over the fleet? No.
People tend to look at recent events and forget what happened in the past. A few years ago Celebrity Cruises had propulsion problems almost monthly, and some times weekly, on all of their ships which used azipod propulsion. It went on for over a year. Dozens of cruises were affected in all.
In 2006 (7 years ago this coming Saturday) , Star Princess had a terrible fire that heavily damaged the port side of the ship and caused a guest to die from a stress-induced heart attack.
All of the Carnival incidents are unique. If there is a common cause it lies in something as mundane as a maintenance procedure or process that is used by every ship, or in a lack of rigor in the quality assurance processes at the shipyard for the newer ships. It is easy to point fingers at Fincantieri shipyard, but then you also need to consider Fincantieri has also built many of the Holland America and Princess ships currently in service. The latter cruise lines have had few to no problems. And despite what some reports say, not all Carnival ships were built by Fincantieri. The Fantasy and Spirit classes were built in Finland by Kvaerner.