PS Yes, insulin sensitivity is vastly improved by fasting - especially prolonged fasting, or even regular IF. One theory is that a reduction of visceral fat (aka 'invisible' or 'dangerous' fat) gives the pancreas a new lease of life. If you think of it in terms of breaking out from its 'prison' of fat, you're probably not far off the mark. I believe there is also clinical evidence that supports this theory, and a www search should turn up quite a few hits on the topic.
Another theory is that the fast gives the pancreas a break, giving it time to repair itself & make more effective insulin, etc. The caveat though is that T1 is less susceptible to these benefits, and even in T2, if the subject returns to the poor eating habits that caused the diabetes in the first place, the benefits will be short-lived after normal feeding has been resumed.