I don't know how it works in the US, but in the UK foreign students pay much higher fees than domestic students and are a significant source of revenue for universities. There may be pressure on academic staff not to jeopardise this arrangement by calling attention to cheating.

There are significant problems with cheating in UK universities too, particularly (but not only) with international students [1].

[1] http://www.independent.co.uk/news/education/education-news/4...