Because they force them. They say if you don't sell for 10% (or whatever number they like), they'll allow a generic company in their country to make it, and the owner of the IP will get zero.
So much for your claim that drug companies collude with the US government to rip off Americans.
Now that you've learned how it works, what do you think?
BS there is indeed collusion with ‘government’. Johnson and Johnson did not donate millions for a Jeb Bush candidacy out of charity.