Because examinations they're passing and all the classes they're not attending are conducted entirely in English only. What I've observed happening in some places is that some specific schools are predominantly populated by rich international students from China and they pay someone else to attend classes and take their exams, or otherwise behave in cheating behavior to get the grade, but they themselves are not attending class or learning anything useful.

It's a scam on both sides and it devalues the degrees.