I make these things at least once a week. I really honestly don't know why, either! There is always a different flavor and the number of ingredient combinations is near endless, but ... it's easier and quicker to just whip up a batch of Poorly Cooked Eggs
HOWEVER, I probably make these things as often as I make Poorly Cooked Eggs. It takes twice as long and requires baking, but ... it's just ... creamier ... softer, perhaps. More yummier? I think because there's more cream in the eggs and that it's baked, mastication becomes a slightly more sultry experience.
Doing it this way also allows you to make more than you'd be able to in a single pan. Portions are also easier to hand out ... they're just beautiful little baked eggy cups of delight!
I also will put them in the oven and go take a shower, while they bake. Out of sight ... I will then refrigerate the remaining little pucks of goodness for another day. They hold quite well and reheat easily!
I do recommend non-stick Teflon pans for this kind of thing. The frittatas pop right out, but in a standard muffin tin ... they're likely get stuck ... and stay stuck, unless you butter the dickens out of the cups, in advance. That's right. The dickens. Another option would be to use cupcake liners.