You greatly overestimate the capabilities of computers of the era that this originated in. Major limitations of disk space, speed and addressability combined with limited CPU power and RAM mean that your hypothetical, “it could have been done” would require a significant investment in development and runtime resources all to avoid having a directory in root that would be empty until after a post-crash recovery.

Also remember that these systems would have all been multi-user time-sharing systems, not desktop computers.

Sorry, but I just don't believe all this. We're talking about hiding a folder. Of course the developers could do that.

well sure, they could have named it .lost+found instead of lost+found, but you’re overestimating the value of hiding it.

It's at the root level, no user came near that back then so it was kinda hidden.