Knuth is famous for focusing on writing his books. He even stopped using email because it was too distracting. I doubt he has the time (or interest) to export all his writing to modern indexable formats on a site he maintains (Prof. Knuth feel free to yell at me about this assumption). He is clearly credited. Just getting the knowledge out there is good.

What I find truly astonishing is that this 1974 paper is so relavent today.