They have high sugar content.
Most of the bananas seen in the U.S. are genetically identical, which means they are ripe for a blight to wipe them out. Banana seeds are incredibly rare.
They are often sprayed with a fungicide (or some other chemical) that is sticky and makes my lips numb and swell if I get it on me. Not exactly sure what it is. Buying organic has solved this for me.
Umm... It might be a neolithic agricultural product, but there are still a few handfuls of wild varieties that aren't quite the same.
I guess I don't really know, and I'm just rambling now.