Anyway, consider the following scenario. Bob makes $10 an hour, and produces $100 of value. Obviously, this is a great bargain for Bob's employer. So much so, that another employer should be perfectly willing to offer Bob $11 to lure him away. Another sweetens it to $12 and Bob moves again. Rinse, repeat until Bob is making $100 minus the opportunity cost.
What that suggests is that a large gap between compensation and productivity is unstable, as large forces will be at work to shrink that gap. So why is inequality happening?
I suspect that productivity simply isn't increasing for a lot of jobs. Such as janitorial services - there's no automation there, the janitor with a mop and a bucket is doing the same thing he's done for decades.
The rise of computers and the internet, on the other hand, have caused the productivity of other jobs to soar enormously. For example, slightly improving the speed of the operation of a server farm can produce millions of dollars in value. I would expect that workers who can do that will be highly compensated for such value produced.
In other words, there's a growing inequality in the productivity of different kinds of jobs.