I stand corrected you’re right

Except the GNU stuff, which has as a design principle "no arbitrary limits". Meaning no limits at all, not "no sane limits":

  Avoid arbitrary limits on the length or number of any data structure, including filenames, lines, files, and symbols, by allocating all data structures dynamically.

I assume they're relying on the OOM Killer and quotas to prevent DoSes all over the place.