our pancreas produces the insulin to act as a exit into our cells to allow the glucose to exit our blood stream into our cells, if you dont produce enough insulin then you have to inject it so that the glucose can escape, if however you do produce enough insulin but our cells are resistant to it, ie the key no longer fits then we must either take a drug that changes the locks (or insulin) so that the glucose (or keys) fits or reduce our weight and do more exercise etc. because that also make us less insulin resistant, the extra glucose not entering the cells is what does the damage running around in our veins basically rotting the smallest capillaries, so if you are insulin resistant then yes indeed injecting more insulin would not make much sense, however if you are fit and healthy the the keys not fitting the locks has to be genetic i reckon, i have zero medical background and only half a brain so please feel free to correct me
also when you insulin resistant your cells are screaming out for glucose but it cant get in but your pancreas dosent know thats the problem so it answers your cells request and produces more therefore wearing out your beta cells because they are working really hard and think sod this im knackered and give in, apparently by eating less glucose and taking meds you give your pancreas a hoilday and it can come back revived from its week in the bahamas and work better than before which is why we do well when we do the right things