Vertical integration has been a common practice in industry for 150 years. Yes, very few firms fully control their upstream supply chains, but very few conversely produce nothing but their core market offering in-house. Most companies are somewhere in between, doing some things in-house, and obtaining other things from vendors.

Most large firms have in-house software dev teams responsible for at least some portion of their development work. I know software engineers locally working, variously, at banks, pet supply distributors, power companies, soft drink bottlers, and many other non-tech industries. And AI can and will extend these teams' capacity to internally manager larger segments of their companies' tech stacks.