Why are oil bubbles when cooking bacon only around the bacon

I render off the necessary fat over low heat, then remove the bacon strips, increase the heat, and fry using the rendered fat. When nearly done, I return the bacon to the pan to crisp it before serving.

Of course, you could also just save the grease from one batch to use with the next, thereby ensuring you always have both fresh-cooked bacon and (reasonably-fresh) grease to use without having to produce the former before the latter.

I believe bacon warps when cooked largely because the different stripes (fat and meat) respond differently to being cooked - the fat doesn't contract as much. So I think that thicker bacon will tend to warp less, because it has more structure and can't curl about as easily, and often higher quality bacon is thicker. But if you got really amazing thinly sliced bacon, I can't imagine it not curling when cooked.

(Disclaimer: It's been a long while since I cooked bacon; I eat little meat and cook less, so I could be wrong.)