First, they do. Second, most software is not only not produced by software startups, it's not even produced by software companies. Do you know how much software a bank, or a credit card company, or a telecom provider, or a car manufacturer (like BMW), or a shipping company (like FedEx), or a defence company (like Boeing), or a large retailer (like Walmart) write in house?
Wasn't the discussion about greenfield projects? Or by greenfield do you mean internal greenfield projects at existing companies that already use Java?