Is icing sugar or caster sugar better for meringue?

Icing sugar stablises meringues and dissolves more easily. Sugar stablises meringues, and the biggest problem with most pavlovas is that people don't beat them long enough to dissolve the sugar. I don't reckon you'll be going back to using caster sugar anytime soon. I certainly won't be. This begs the question: why not just use a sugar like icing sugar that dissolves more easily? There seemed to be no reason at all why people haven't been using icing sugar instead of caster sugar to make pavlovas other than just "it's always been done that way".