https://en.wikipedia.org/wiki/Rent-seeking
Which isn't to say we aren't worth it; I'd like to think we are. Just that we often delude ourselves into thinking that our salary differential is linearly correlated with the economic "value" we generate. It isn't.
Or rather: the "value" of an engineer is a lot like the value of an apartment in a high-rent neighborhood: the price holds in the market because, well, you have to have it, and at (almost) any cost in order to do all the other stuff you need to do, like get around the city and be close to your job.
You also have to have access to food and safe drinking water -- even much more than you need a convenient or semi-stylish apartment. The priority for these isn't just a bit higher: it's categorically higher. Yet their base cost (i.e. the cost to obtain them at nominally satisfactory level) is an order of magnitude less than the cost of your rent.
The distinguishing factor between the two classes of goods is, of course, scarcity. That is why your rent is damn high.[1] And that's why an average software developer can earn twice as much as a decent chemical engineer, and an ungodly multiple of what a great public school teacher makes.
[1] Along with the fact that high-demand apartments -- like high-demand engineers -- are also, arguably, Veblen goods in some markets:
https://en.wikipedia.org/wiki/Veblen_good[1] http://work.chron.com/salary-petrochemical-engineer-4334.htm...
Comparing with my friends who are still doing ChE jobs, If I was still in petrochemical, I most probably be getting paid little less than what I am being paid now, but working much more harder, longer and more stressed.
Ok clearly I am out of touch then. But seriously, how many SE really gets paid 250k+, even at Google? Quants is in my mind the same as the petrochemical industry tough, rediculous salaries so that one I can believe.