These arent DnD tropes though, theyre tropes across ALL fiction
Atlantis was a fallen advanced society, Indiana Jones and Tarzan were exploring all kinds of lost dungeons and well Fairytales are all set in the same “Once upon a time in a land far far away”.
And Dungeons in DnD worlds actually do make a kind of sense - commoners arent going to be keen to strip building materials from a haunted ruin when theres a real chance of being killed or eaten by monsters.
Unless you mean the video game at no point was the ancient civilization more advanced in Indiana Jones than the current one. Neither is this a usual theme in fairy tales. The only other fiction where this is a common theme is SciFi with precursor civilizations. And at least in most SciFi there you do not have static societies which stayed the same for centuries without any technological progession unless it is the central theme of said fiction.
In D&D nothing ever progresses period, just because they wan't to keep everything at pseudo medieval level but also have centuries of history.