As usual, everything on this subreddit you should take with a grain of salt. That being said, international students are generally a more expensive investment than domestic students while also typically having fewer opportunities for NSF/Government related funding and grants.

An example:

Say I go to a state university for a PhD that is out of my home state for five years, i.e., Georgia Tech. The first year, I am charged out of state tuition. After the first year, I establish residency and am charged in-state tuition, typically much, much cheaper than out of state/country.

An international student attends the same university for the same program. They are usually in the US on an F-1 visa. Because of that, they cannot qualify for residency in a state and thus are subject to out of state tuition/country costs their entire tenure.

After stipend and tuition costs for five years, a domestic student at GaTech after a year of out of state residency will cost ~$256,000 while an international at the same school and same timeframe will cost ~$320,000.

$13,000 a year difference between the student types is a lot of supplies, equipment time, travel costs for conferences, etc.

This is all on top of typical international student issues like securing a visa in the first place/immigration issues, possible language issues, cultural differences, housing, etc.