Exploring various Acient Nordic ruins it, i cant help but notice that there architecture far exceedes the current nord one.There Buildings look way more impressive, they have all kinds of lifts,puzzled doors and so on.Then there`s there medicine who judging by the way they buried there dead its more advanced all.Literature also, there`s hardly any Nords scolars at all.

Magic i think it has something to do with Dragon Priests?As in they where the only ones who where practicing it?Anyway why did they get dumber over time?

Possibly, the Nords are hot headed and instantly blame something when things happen or group people in together without hearing from another side i.e. Child abductions are caused by Falmer, The College is responsible for the great collapse, all Elves work for the Aldmeri dominion, all conjuration experts are necromancers, all destruction experts are evil wizards bent on destroying town. The Nords really do seem to be a lot more stupid in the 4th era but there are still some that listen to reason and aren't as hot headed as most of the idiots in skyrim

The Barrows were once Temple Compounds for the worship of the Dragon Cult. It's understandable after the Dragon War that the Nords would want as little to do with those structures and their styling as possible. Modern Nords even maintain an ancestral awareness to their ill past, since none of the NPCs you talk to like them or are even eager to go explore them.

Medicine is debatable. The Draugr aren't so much embalmed and entombed so much as they are buried alive as living batteries for the Dragon Priest/Warlord that also resides in the tomb. The presence of embalming tools is a bit of a mystery after that revelation.

Literature? Nord tradition is the Song and Poem, not long winded books. You want Nord History? Look up the Bards or one of the books that collects the "Songs" of Skyrim. Plenty of Nordic traditional and literature - just put in a different style then what we're used to.

Magic has been a part of Nord life for a long time. It's only in the past few hundred years that Magic has fallen out of favor in Skyrim, and that could be a natural reaction to the magical nature of the Oblivion Crisis and Baan Dau's fall which triggered the Red Year. Then of course there's the Great Collapse of Winterhold...

Yeah, Magic hasn't exactly been smelling like roses in Skyrim for awhile.