Maybe they have and it's just that most Nords don't watch the Skyrim Histoory Channel.
Maybe they emulate our culture and far more watch "Desperate HouseCarls" than more knowledge expanding fare.
ha, so here skyrim has all these myths about dragons, they got that mysteries dragon bridge by Solitude, they have the power of the voice, ect ect ect, and Nords are more than mere nomads clubbing at aminals, they build castles and are very civilized. Also, you have many people trying to get rich by raiding tombs and caves, yet not one person digs up a mound? and if they did they wouldn't show the bones off to every Jarl in the land to try and attrach some coin for being teh first to prove teh existence of dragons? Sure, it was an obvoius brain fart on part of the devs lol. Not that i care cause its not a game breaker. I just find it funny that the devs allowed the mounds to be so obvious.
It would be like us wondering if Aliens really existed but never bothered to investigate any UFO crash sites with dead Alien's bodies rotting in the sun for all to see but none would look...