Advances in naval automation allow fewer meat-sacks, and advances in manufacturing automation make equipment relatively less expensive than meat-sacks. That's Baumol's cost disease in action, again. It turns up all over, doesn't it?
Traveller consciously ignores Baumol's,* asserting a universe where sophonts are still important, and not replaced by automation. If drew a lot of inspiration from the science fiction of its time and before, and almost all science fiction featured important roles for humans (and other sentient living beings). Additionally, it's a role-playing game; the lives of the humans on the Axiom in WALL-E are not the stuff of fun role-playing.
* Or maybe none of the creators of Traveller were aware of Baumol's, or perhaps it was not a solidly-enough established economic principle by the early 1970s for it to be a part of the curriculum at Illinois State University, where many of the founders of GDW went to school.