[colejohnson66]

Well, Knuth still writes all his stuff using "plain" TeX. For example, the source of the TeXbook and the METAFONTbook are both TeX, not LaTeX or whatnot. Granted, he did create TeX, so he's probably more comfortable with it.

[ilayn]

Pure TeXnicians are a thing. Besides, what do you expect him to use? it's his creation.

The point is he created TeX for himself and expected others to supercede it with a proper implementation. Didn't happen though.