Re: Companies probably aren't doing this to discriminate
They are doing it to maximize their advertising dollar. If you are advertising for an oil field worker, you are getting far less of your money's worth by advertising to women, or to men over say 50 years old...
What you just wrote is basically a pure capitalist justification for racism / sexism / ageism / whatever-ism.
It doesn't stop it being sexist just because you're doing it for financial reasons.