When do y’all think the sea change was, the turning point, when software stopped being “done”, and people started believing that if there were no updates, or updates were infrequent, that projects were considered abandoned or dead?

Because it didn’t used to be, not for literally everything. OSes, yes; DEs, Feature programs, suites like word processors, sure. But you got awk, and sed, and they were “done.” You didn’t expect updates to old, established code. I only just realized this because I was surpassed gettext got an update. I’d have expected it to be baked software.