I'm the the go-to guy at a small government agency for the overall network/system architecture. There are some technical & memory-related prereqs (i.e. I have a CS degree, and I'm not a dummy), but mainly I know our systems so well because I've worked actively on them for more than a decade.

It would probably take me a decade to build such a detailed mental model at another company or agency. And that's even assuming I could get hired. One consequence of working on an idiosyncratic, one-off architecture is that my mainstream tech skills have atrophied significantly. I definitely could not pass a leet-code interview at a FAANG anymore.