Y'see, to me, I wrote them because I was bored one summer between as I was shifting between colleges. There's no glorious backstory regarding the origins of the fic.
So, I ask, what drew you to the series?
Well I suppose the concept of Lisa and Maggie being the same age is inherently useful since they can have a conversation which doesn't involve pacifier noises and gestures. It's hard to convey complex concept and nuances without speech.
As for why I like the series I'm a long time fan of the FF series and The Simpson's. Go figure.
Actually it always seemed odd to me that there was never a Simpson's RPG since so much of it's humour is dialogue based, that would fit really well with RPG's or point and click adventures. Still if South Park:The Stick of Truth does well who knows maybe they'll make one.