The practice of looking up algorithms by name dates back to that same time. The phrasing of the law, since they were treated as munitions, was that you couldn't even export something that was designed to have crypto bolted on. So you made it so anything could be bolted on and some of them just happened to be crypto.

The legacy being things like the blacklist/whitelist discussion we had the other day about case sensitivity in crypto algorithms. We still look up algorithms by string name (instead of enum or some other mechanism) decades later.

But books had exemptions and you could export crypto as long as it was printed on a book