For Master's degree it makes sense because the students pay tuition. For most PhDs, the students don't pay tuition and get an additional stipend, so it doesn't

For Master's degree it makes sense because the students pay tuition. For most PhDs, the students don't pay tuition and get an additional stipend, so it doesn't make sense. Plenty of (most?) PhD grads stay but we are currently paying international students to do their PhD and then provide very little incentive for them to stay afterwards.