I expect this is mostly because there is less funding available for students pursuing a Masters. If you can get funded by doing research or teaching, then the ROI of a masters is not bad for US students. It is typically 2 years and many employers treat it as work experience.

This is different for PhD students because you are talking about a potentially much longer period of time and much less ROI. This is especially true given the oversupply of PhDs in most fields relative to the number of actual tenure-track positions. If you can't get a tenure-track position, then you are probably over-qualified for most industry jobs and wont get much more compensation that someone with a masters.

For non-US students, the return is getting into the US on a visa and getting a post graduate technical degree from a US institution, both of which are much more likely to land you a US job (and probably wont hurt your chances in academia / industry in India / China either).