In theory, it's because we're going to be better at steering an LLM in some ways. A lot of the friction and hold up in building comes in the communication between people/departments/organization. If you eliminate that by holding the knowledge in one person/department, you see an efficiency gain.
What they're not saying is that they think we're more valuable because they think we'll be cheaper. They think they can have us do 2 jobs and pay us for 1: probably less than a decent SDE made in 2019.
Personally, I think it's likely to be a shitshow and backfire if that's how companies decide to try to go that route (especially the largest ones). First, if we wanted to be devs, we would be (like you). Most people with the knack for programming and thinking in systems know they have that knack, and if they haven't jumped ship to SDE before now, there's a reason. I could definitely hack a junior SDE role, skill wise, but I don't want to. Second, finding people like us is difficult. The hiring process (which is becoming more and more Gilliamesque by the day) is really bad at identifying us. There aren't credentials, and this sort of work tends to reside in the gaps, as you identified. It's harder for it to show up on a resume. Hiring is optimizing for exact matches and experience, and that's the opposite of how this skill set actually functions. I've found these skills are best developed by being placed in a room where you know very little about what's going on and forcing you to develop heuristics and approaches over time for getting that context. Thirdly, I can't speak for you, but I've developed this perspective over decades and if people want it, they're going to pay appropriately. If they think I'm going to do any of this at my current salary level, they're deranged. And lastly, while most people in our position might roll our eyes at some techie discussions and culture, we do fundamentally like techies/devs and we tend towards placing a greater value on things like relationships than a pure SDE does. (Just speaking in generalities). So 'is willing to replace and/or toss out a category of people I like and respect' is a hint to us to start out assuming this is a hostile negotiation. (Whereas SDEs as a cohort over the last 20 years extended a lot of goodwill at first). We're far more likely to work somewhere, get enough domain knowledge, and then bounce to start our own thing, especially since as a population we're more likely to have devs who will work with us as non-technical founders. Someone who's decent at marketing/sales/the stupid 'people stuff', understands a domain, and understands when a proper dev tells them what is and isn't possible and can even help with some of the most boring, rote parts of the technical side if needed/in crunch is an excellent non-technical founder, and as a group we're also more likely to have access to the technical connections that we'd need if we wanted to build something beyond our ability.