The bulk of software that is actually making money and not just trying to convince investors to get in early enough to get rich off of other investors before enough people figure out they're never going to monetize are still selling to enterprise customers. For every 30 people figuring out how to profit off a user-facing web app, there are 3000 chugging away at basic J2EE or maybe Spring Boot now for some proprietary backend business system for a Fortune 500 or the government that no member of the public will ever see. This sort of work seems to have become invisible to web-based developer communities like Hacker News, but they're still there. The need and the demand has only grown.
Granted, I don't know that it means there needs to be dedicated Product Manager roles. Granted, I as an engineer don't particularly want to deal with expectation management, scheduling, and capacity planning, and am perfectly happy to let someone else do it, but most of my work has been for the military and intelligence community and I think we have a much bigger problem there that org structure at the actual product development level can't solve. Our "customer" is an acquisition office, not the actual users of our products, and we're not legally allowed by the structure of contract law to have any direct contact with the actual users. So we cargo cult the hell out of basic agile principles that promise a more responsive and user-oriented process, but we can't legally implement that process the way it is actually supposed to be implemented. Instead of being directly accountable to our users, we're instead accountable to career bureaucrats who are more concerned about adding bullet points to their resumes while taking minimal risk than the actual needs and use cases of analysts and warfighters.