Fun thread, all in all. The reason I prefer doing oatmeal in the microwave is purely personal and I certainly am not trying to convince anyone who's happy with how they do it - just sharing!

Anyway, the reason is that it's fast, I don't have to watch/stir, and I only have one vessel to wash.

I've not tried making a large batch and reheating - might do that. Oh, plus DH doesn't like oatmeal so I'm already fixing two cereals. I don't - btw - fix any other hot cereals in the microwave as they lump badly, they need the constant stirring. DH like cream of wheat or Maltex, or actually any other cereal than oatmeal.
And the person who asked, why not instant? - ick, it's a toally different product, and to me doesn't taste like oatmeal at all. I've eaten it in a pinch, or camping, but it's way down on my list of "things I like to eat."