There are many format and human language you could write the date into. And many timezone.
By putting timestamps in log files, and requiring humans to type a few more keys to transform it when they need to, every one can choose its date format, timezone, and language. So, to me, djb's way is the human-friendly way.
I agree. Further, all kinds of tools use logs in different ways and often need decent CPU power anyway. Making logs efficient & machine-readable by default aids that. It also lets me use lower-cost components for services producing and storing them. This goes same for lightweight, high-performance services like we've seen show up in HTTP. So, instead of one bulky server for several grand I might have several, embedded boards in a H.A. configuration with plenty of memory and storage doing same workload.
So, efficiency still matters today if you're squeezing the most out of your systems or like physical isolation like I do. Easy, portable processing on arbitrary machines, too. Human readable logs can have an impact on that. A nice compromise, though, is stuff like JSON, s-expressions, or a TCL style with abbreviated keywords.
By putting timestamps in log files, and requiring humans to type a few more keys to transform it when they need to, every one can choose its date format, timezone, and language. So, to me, djb's way is the human-friendly way.