Robots are widely deployed in manufacturing, just not humanoid robots. The biggest benefit of stationary robots is that their behavior is 100% predictable and they are always where the humans expect them to be. There are certain areas in factories which can be nearly 100% automated (pick & pull in warehouses, for example), but there are a lot of areas where, without a human in the loop, there are too many edge cases to reasonably expect humanoid-robots-as-replacements-for-humans to anticipate or react to.

(I have 15 years experience in high tech manufacturing, with most of that building test automation & manufacturing execution systems, and an advanced degree in operations research.)