Because people from poorer countries like these use their employers computers to download movies, games and music from p2p networks. The Westerners have more disposable income so they a) use their own computers for entertainment and b) buy stuff from amazon and itunes instead of searching for warez.
So its about income and culture. Company cars are also viewed as a perk and its not unusual to take a company car for a picnic.
Employers are usually fine with this - it improves morale and is less costly than actually paying more.
s|movies, games, music|games/software| and it might be more plausible. (.mkv, .mp3 or even the .rmvb that's weirdly popular in China are hardly common attack vectors.)
However, if we're talking about China, and the demographic of employees that get sent for international matters, then we're definitely not talking about people that can't afford their own computers. I would posit this holds for nearly any country (except North Korea?)
Taking your argument as just "a culture of grabbing untrustworthy software from anywhere is the reason", it becomes more persuasive to me.
So its about income and culture. Company cars are also viewed as a perk and its not unusual to take a company car for a picnic.
Employers are usually fine with this - it improves morale and is less costly than actually paying more.