The problem is that we do have formats that do work for long term archiving, but are limited to a platform and are not open, so decoding them in the future may be problematic.
WinRAR is one example. It has the ability to do error detection and correction with recovery records. However, it is a commercial product.
PAR records are another way, but it is a relatively clunky mechanism for long term storage.
Even medium term storage on disk/tape can be problematic:
There is one standard for backup programs for tape, and that is tar. Very useful format, but zero error correction or detection, other than reading and looking for hard errors. There are tons of backup programs that work with tapes. Networker, TSM, NetBackup, and many others come to mind, all using a different format. Of course, once you get the program, there is still finding the registration key, and some programs require online activation (which means when the activation servers get shut off, you can never do a restore from scratch again.) We need one archive grade standard for tape, perhaps with a standard facility for encryption as well.
Same with disks. It wasn't until recently that there was any bit rot detection in filesystems at all. Now with ReFS, Storage Spaces, ZFS, and btrfs, we now can tell if a file is damaged... but none of the filesystems have the ability to store ECC on an entire (other than ZFS and ditto blocks.) It would be nice to have part of a filesystem be a large area for ECC on a block basis. It would take some optimization for performance, but adding ECC in the filesystem is more geared for long term storage than day to day file I/O.
Finally there is paper. Other than limited stuff on QR codes, there isn't any real way to print a document onto paper, then scan it to get it back. There was a utility called Paperbak that purported to do this, offering encryption, error correction, various DPI codes, and so on. It printed well, but could never scan and read any of the documents printed, so it is worthless. What is needed is something like the Paperbak utility, but with a lot more robust error detection (like checking of blocks are at an angle similar to how QR codes can be scanned from any direction.) This utility would have to be completely open for it to have any use at all. However, if it could be done to print small documents to paper, it would help greatly in some situations, such as recovering encryption keys, archived tax documents, and so on.
Ironically, in general, we have the formats for long term storage. We just don't have any that are open.
Hardware is an issue too. Hard drives are not archival media. Tapes are, but one with a reasonable capacity is expensive, well out of reach for all but the enterprise customers. It would be a viable niche for a company to make a relatively low cost tape drive that could work on USB 3, has a large buffer (combined with variable tape speeds to prevent shoe-shining), and has backup software with it that is usable and open, where the formats can be re-engineered years down the road for decoding.