What if the companies that were placing job ads on Facebook were also placing job ads on other platforms that weren't targeted to men only? Playing devils advocate here...
It only be an apt analogy to the Universities if Facebook were some single-gender social network. Or if an all-gender University let you only recruit one gender.
But in general, there are classes of ads that you just can't target based on certain classes, period. Even if you hypothetically might have the ability to target a counterbalancing ad somewhere else. Facebook repeatedly has been in hot water over this, and both they and the people using their ad platform to do this stuff need to get more than a slap on the wrist, in order to deter others from trying the same in the future.