Want to know the reason?
- Finance people are wealthy
- Finance people's money works for them, instead of the other way around, so they aren't constrained by 9-5 jobs
- Finance people are on other boards, and know other board members and politicians, and have reciprocal arrangements--official and otherwise--with them
- Between "having the free time" and the network effects of "all my friends are here",
The same applies to Law, frankly.
It's the same reason our political class is dominated by law and finance, and why labour of any kind if highly underrepresented: they're the professions of the idle rich. If you work a day job--even medicine!--good luck taking the time off to do something like running for office or working on multiple boards.