Mike Ravine of Malin Space Science Systems explains for Digital Photography Review:
“There’s a popular belief that projects like this are going to be very advanced but there are things that mitigate against that. These designs were proposed in 2004, and you don’t get to propose one specification and then go off and develop something else. 2MP with 8GB of flash [memory] didn’t sound too bad in 2004. But it doesn’t compare well to what you get in an iPhone today.”
In addition, Ravine cites the data transfer rate from Mars and familiarity with similar systems in the past as contributing factors to the choice. It’s quite incredible to think that space craft are thought to be some of the most advanced objects ever created, but they really need to be simplified as much as possible. It’s a whole different world on Mars.