Yes.

In a wider sense, you also want to explain why something is NOT done. Ie why certain other ideas don't work, or why we don't offer certain features.

Same idea should apply to laws. The why gets forgotten a half century later because the problem was solved but not well documented. Because the problem is no longer happening, they think the law must no longer be necessary.

As a counterpoint, we often end up with laws, traditions, and social mores that long outlive whatever rationale they had for them in the first place. (Assuming they had a rationale, and weren’t just based on fear and superstition).

That someone being me not knowing why in hell would I write this monstrosity... git blame + some archeology work to get jira ticket number (I put issue numbers in commit message/branch name) and from that I know why.

Yes, naturally "those who come after" often includes the future you.

Much of my life as an older dev includes balancing my relationship with my past, current, and future selves. Be kind to your future self; be compassionate of your past self. And don't forget, they really are different people ;)