The Cyrodillian Empire has forgotten its roots because Medes isn't of Nord blood. He's an Imperial. His concerns are understandably more aligned with where he was born and the people he considers his own. But that doesn't mean the Nords didn't start that Empire. It means that Empire forgot it.
They're probably going to be reminded in upcoming DLCs.
Er...I hate to tell you this...but theres actually no proof that Talos was a nord most references place his birth in High rock and his description of being as tall as a breton and aging as one kinda means he could've been a breton. He didn't even get the name Talos until after the battle of sancre tor where he somehow got the nords on his side and they gave him the name Talos.