I think specialising in brownfield has always been a thing. If anything, it's greenfield that's the rarity.
Maybe vibe coding replaces some pioneering work, but that still leaves a lot for settlers to do.
(I admit I’m generally in the settler category)
https://blog.gardeviance.org/2015/03/on-pioneers-settlers-to...
Perhaps the old adage "it's getting hard to find X employees [at the price we are willing to pay]" applies.
That surprised me because I've seen articles and heard podcasts for years where they've said COBOL programmers are well paid due to scarcity, though never quoting amounts.