For those of you asking what the Koreans did wrong (in good faith), that question is framed poorly.
There is simply no visa that allows skilled labor to come to the US, work a temporary job for a multinational that's paying them in their home country, and leave.
The closest thing apparently is the "B-1 in lieu of H-1B"[1] and guess what? Another commenter posted this FT article that accuses them of abusing this B-1 visa [2].
Traveling for work is a huge pain in the ass, doubly so for this sort of temporary work assignment, and triply so if it's to the USA.
I've always been told to use a tourist or family reunification visa. For example, if China cracked down on this, they could easily put 10,000+ Americans in jail for a similar "visa abuse". They obviously would not bite the hand of foreign direct investment like this though.
I think it's informative to interpret the law - especially in the age of Congressional gridlock - as 300 years of terrible legacy code papered over the Herculean efforts of ops teams (the government bureaucracy). When that ops team starts arbitrarily treating the oceans of gray zones to their whims, to reward friends and punish enemies, you start the long trek to serfdom...
Finance (I'm thinking prop trading) seems different from Valve. You eat what you kill - if you're sabotaging team members you're not making money.
If you're at Valve, you can count on your monopoly still printing money while you carve out pieces of the pie for yourself. Any negative effects from your work will be felt years later when you're long gone.
That's OK.
They have no idea my sub-region of California produces the entire GDP of their country.