There are nasty surtaxes on salaries over a certain amount.
This drives money from salaries to bonuses.
There are more taxes for cash payouts. This drives compensation towards stock options.
Both were the result of federal attempts to use the tax code to stop CEO compensation increases. People tend to find ways around regulations and rules intended to restrict their behavior.
It works for non-CEO compensation, too. For much of the last 20 years wages have remained flat. This is news. But compensation for a lot of jobs has increased because pre-tax/non-wage compensation has increased. So at my job I get paid a salary, but every year my compensation goes up even faster because my employer covers increased health insurance costs. (They could pay me the additional money so I could pay the insurance premium increases, but I'd be taxed on that additional pay amount. The result of this quirk in the tax code was to drive money into better health insurance plans, which then were castigated as "cadillac" plans.)