2003 Mazda Tribute catalytic converter

I purchaed the vehicle 2 years ago and this is the 3rd time the catalytic converter needs to be replaced. Shouldn't the Mazda dealer be looking at the coils or plugs before the 2nd converter was put in. I'm being told that this is going to cost $3000 to be fixed. Shouldn't the mechanics have done an analysis on why a 2nd catalytic converter was to be replaced in a short amount of time before it was installed.