There were thousands of documents in total but only a comparatively small number of them (around 100) were classified.I could understand a few documents going missing but dozens of boxes with thousands of documents? Seems like the secret/classified document thing is just a meaningless facade.
For instance, if you look at the photo in the indictment of the box that had spilled its contents onto the floor, some of the "documents" were just newspaper clippings of stories about him.
While it's normal for Presidents to have (and subsequently keep) boxes of documents, it's not normal for that to include quite so many that are classified.Apparently (I read online somewhere) it is quite normal for Presidents to have boxes of documents for their personal use, some of which they keep.
As stated in the Washington Post article below, Trump had a particularly cavalier attitude to handling classified documents. As it says, he routinely took classified documents that had been:
used in his intelligence briefings to his private residence with no explanation, and aides sometimes lost track of the sensitive documents.
Trump’s disdain for intelligence rules foretold his indictment