From the very first time i played skyrim till the end of the 9th playthrough i always wondered why they even bothered witht the doors in the nordic ruins becase they were so easy to figure out I saw it more as a waste of time, but then i came accross a book called the Death of a wanderer (page 191 if you have the printed skyrim books vol 1 the histories) which speaks about this in a very interesting way. basically what it says is that the doors aren't meant to keep people out they are meant to keep the draugr in. the book describes how the draugr are incredibally stupid and since the rulers of those ruins before they died wanted to make sure that people visited their grave not some half witted draugr so they made a locking mechanism simple enough not to give a living person any challange but to also make it impossible for the draugr to accidentally open the door. and that is why you will never find draugr beyond the stone door with the dragon claw in the Nordic ruins.
~Credits to Bjorn Yngoll