Actually, Knuth first wrote TeX in SAIL (1977–1978), then discovered everyone was interested and rewriting it for their own systems in divergent ways, so he rew

Actually, Knuth first wrote TeX in SAIL (1977–1978), then discovered everyone was interested and rewriting it for their own systems in divergent ways, so he rewrote a "portable" version in WEB (Pascal) (1980–1982), and he did indeed leave it at that, a few years later (https://tug.org/TUGboat/tb11-4/tb30knut.pdf https://tug.org/TUGboat/tb11-4/tb30knut.pdf). It's not that he's easily distracted; it's just that he really cares about quality, and underestimated how long this detour would take. :-) (He told his publishers in March 1977 that he'd have proofs for them in July; he was expecting it to be a month or two of work; not 10+ years.)