There are reasons for this oblivion, not all of them bad, and far more powerful reasons for rescuing the city from the condescension – or worse – of posterity.
The first and most obvious reason for the neglect of Thebes is the existence of the Egyptian city of the same name (situated within modern Luxor). Capital of Egypt during the New Kingdom, the era of Rameses the Great, it is far the better known of the two namesakes today. (There was yet another ancient Greek Thebes – but one that is eminently forgettable.)
Second, Thebes only briefly drove the political agenda – between 371 and 362 BC it established a brief ‘hegemony’ – unlike the two Greek cities that have hogged the limelight for millennia: Sparta and Athens. It was precisely because Sparta and Athens conspired to keep it that way that Thebes was forced to languish within the deep shadow of their bright incandescence.