greed. the patent was donated to the public domain back when synthisis was discoverd but since the manufacturers have taken up tweaking it patenting that tweak then charging more and more. other countries dont have this problem with insulin. thats why you hear about people going to Canada and Mexico to get meds cheap.
"old insulin" pre-~1980 was made from grinding up animal (cow, pig) pancreas and extracting a tiny amount of pure insulin through a chemical extraction process. Wikipedia posts a ratio of 2 tons of animal matter to 8 oz of insulin. It was "easy" but didn't scale up very well.
