Hi Patch,
There can be many reasons why type 2s are prescribed insulin. In some cases their pancreases might not be able to produce enough insulin so it needs to be supplemented, or they may have followed the government healthy eating guidelines and as a result have blood sugar levels and insulin resistance that is so high that insulin becomes the only possibility, or they may have a GP that simply isn't aware that there is any treatment other than insulin (fortunately not too many GPs like that but there are some out there as some of our members can testify). There are also some people who decide that they are not going to let diabetes change their lifestyles one little bit and continue an unhealthy eating pattern that will inevitably lead to insulin as their only possibility.
Insulin resistance remains a problem for them whether the insulin is injected or self-produced, so they also usually need metformin and/or glitazones.