The employers pay as little as possible to get 'enough' output for steady growth and then keep all the increases.
Employers don't set wages. The employers pay wages that are defined not by the employers, but by the supply/demand balance in the market for the workers that can do the job.
If lots of people can do a job (such as low-skill labor), the supply exceeds the demand and drives down wages. If few people can do a job (like highly technical or complicated things like, for example, neurosurgery), the demand exceeds the supply and drives up wages.
You're right, of course, that the employers want to pay as little as they can. To pay more than they have to would be, well, stupid. But how low they can get away with is dependent on market rates.
Different businesses also do different things within that... For example even in a low-skill job like fast food, In & Out here locally is known for paying wages above and beyond what is typical for fast food joints. They make that choice because of what they get for it--access to higher quality workers than their competition, lower turnover rates, and better employee morale.
You may view labor through the lens of "exploiters vs exploited", but as with everything, it's always a lot more complicated than you think.