We make things, we don't manage people. As such we are below the people setting wages.
Yes, engineers are professionals and all that, but we are seen as the executors. The final rung on the ladder who finally executes and builds the thing.
So our wages do not scale that great with value of output.
In many cases we are factory workers, maaaybe artisans, in a feature factory --> https://hackernoon.com/12-signs-youre-working-in-a-feature-f...
If it makes you feel better, in MBA speak you're a "direct contributor" (unlike everyone else who has to justify the value they supposedly provide) and all those suits are stuck in the "overhead" bucket (i.e. "a burden, not contributing to revenue in any way").
Doctors and lawyers are direct executors in a sense. Do they have a similar problem?
And I would differ with your assessment that tech wages scale poorly with productivity. Better than many other areas, engineers can leverage their productivity extremely well - especially in software, but even moreso in the future with information and mechanical automation becoming ever more capable.
Doctors and lawyers have controls in place to limit the supply of labor.
Edit: clarified real wage to real wage vs productivity.