TB will tell you.
It's so that the pharmaceutical companies can afford to develop the new drugs they so graciously sell to foreigners at a loss.
And purchasing drugs out-of-country doesn't help the drug companies subsidize the token free drugs for those poor people without insurance who can't see physicians to prescribe them.
Damn decent of them. Doesn't explain why US citizens can't buy foreign drugs in foreign countries but what the hell.
Arf