There are different things you can do to affect texture with the wrapping. For instance, some microwave paninis come with a special plastic-foil thing that helps crisp them (they're still inedible because of the sodium content but they are crisp). I imagine it'd be hard to make crispy and a steamed soft mushy food at the same time, which holds them back from using it in full meals.

Also some of the complicated steamed or crispy microwave meals produce so much garbage it's embarrassing to cook them.