Two decades and you don't see any value in writing down what's currently in your head?
Anyhow, ADRs are good, but they stand for Architectural decisions, not every decision is at that level.
In general, if there's a better place to store explanations, do use it, but often, in many projects, commit messages are the least bad place; and it's enormously better to write there than nowhere at all.
Line comments work pretty well for explanation storage. :) Almost every programming language support that feature.
They can sure be good, and are often indeed a better place, but unfortunately most people don't want too many lines of comments in the code.
We sure should have better tools to handle code annotations, but commit messages are a not too bad fallback until we get them