Definitely a result of being fatter than they are in the wild, which is probably true of most captive pythons, but easily evident in a monochrome animal with very small scales like an Olive. Adult Olives eat large meals, probably very infrequently, so a feeding regime of many meals throughout the year, for a generally large and inactive snake, is what causes them to become very overweight. We have a largish (2m) intergrade python which has lived in our shed for the last 3 years. I see her at night through the summer, hanging down over my rat cages. I know where she hides through the day so I can check her occasionally. Last year I saw three occasions when she had eaten something big enough to give her a bulge (probably a wild rat), and this year 4 times. So, given that I might have missed a couple of meals, she is probably eating a moderate meal once every 4-6 weeks, which I suggest might not be unusual for a wild python. I suspect that large wild pythons we see in the bush might be a lot older than we think, given that their growth rates are related to food intake.
Jamie