I'm running Bosch 9607 Fine Wire Double Iridium, these are gapped at 0.44 (1.1mm) and seem to work very well. During my research I read the simple copper plugs are gapped tighter to achieve a longer lifetime as continuous wear increases the gap over time.
But the tight gap is supposed to have some disadvantages, so copper plus improve over time to reach their optimum capabilities before "fading out".
Using rare earth plugs allows less wear so the gap can be chosen more optimal without losing lifespan due to wear.
So, long story short, the wider gap of (double) iridium or platinum plugs is because the wear slower than copper. That's what the internet said
. Leave it to the pros here to confirm or reject my words.