One thing I don't understand is, what is preventing anyone from just starting a new factory or importing insulin from abroad to sell it cheaper than the competitors?
One of the huge problems with making generic drugs is that you need to demonstrate that your drug does the same thing as the real deal, which isn't as expensive as phase I, II, and III trials for bringing a completely new product to market, but it isn't cheap, fast, or easy. Likewise, setting up proper facilities to manufacture your product isn't cheap, either.