they do, until they get insulin-resistant because at first the pancreas tries to compensate high blood-sugar with more insulin. eventually the cells simply don't respond to the insulin anymore (which tells them to open up and use the sugar), to which the pancreas responds with even more insulin til it just wears out and stops producing insulin altogether. diabetes progress is all about producing more insulin til your pancreas dies realizing no amount of insulin can compensate for shit eating habits.
Austria