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?

i can't speak to the others but banking and healthcare is virtually all java top to bottom. The big healthcare EMR/EHR systems are Java and every bank i've ever worked with (i use to do a lot of integrations with the big banks) was all Java. I have friends in those areas and whenever they start up a new project it's still always Java since that's where their skills are and what's on the "approved tech." list.

From what I see, most software being created in these spaces isn’t made by startups.