How do you differentiate between "actually abandoned and probably dangerous" and "actively maintained, but updated only very rarely, because there's nothing left to do"?
By reputation, adoption, type of changes being made (e.g. "implemented correct alphabetical ordering with proper normalization" is less mature than "updated to latest Unicode standard, Cypro-Minoan is now allowed"), update schedules (e.g. once or twice a year right after someone opens an infrequent issue vs. once or twice a year during the maintainer's vacations), type of issues that remain open (e.g. "crashes if the description is too long", answer "use a shorter description", is less mature than "bad-looking text wrapping if the description is too long", answer "default column widths are compact, but you can customize them").