I think part of that is how these sorts of businesses choose to organize their money. A manufacturer might budget themselves to be quite lean, so lean that for any sort of improvement like automation with robots, they have to hire an expensive consultant to tell them they have to hire an expensive robot company to build them expensive robots with expensive service contracts. So of course in that model the human is cheaper. However, if the manufacturer instead took all that money they would have spent on the expensive consultant, and opened up their own "internal" automating wing that would just look for things within the company to replace with a robot they create and service internally, maybe the math would pencil out another way.
It's really common to see jobs that people are doing that appear to be easy to replace with robots. But if you actually try to develop automation to do it, you very commonly hit a bunch of gotchas that make the automation infeasible. Sometimes this is a systemic thing (you can't effectively automate this without having to change too much of the rest of the process at the same time, which makes it economically a nonstarter), but more often than you'd think it's because there's an aspect of the job which doesn't seem particularly hard or important because humans do it without even thinking about it -- but to computers and robots, it's incredibly difficult.
